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Evaluation of the Gossypium Gene Pool for Foliar Terpenoid Aldehydes.

The malvaceous tribe Gossypieae Alefeld, which includes cotton (genus Gossypium), has distinctive lysigenous glands containing terpenoid aldehydes (TAs) in vegetative and reproductive plant parts that uniquely delineate the tribe (Fryxell, 1979). Cottonseed is a rich source of protein, but its use for human consumption or animal feed is limited by a common TA, gossypol, in the seed glands (Boatner, 1984). Gossypol is toxic to mammals, birds (Berardi and Goldblatt, 1980), and cotton insect pests such as Anthonomus grandis thurberiae Pierce (Bottger et al., 1964) and Heliothis spp. (Lukefahr and Martin, 1966).

The discovery of other terpenoid compounds related to gossypol in the roots and stems (Bell and Stipanovic, 1977) and in the foliar glands of cotton (Gray et al., 1976; Stipanovic et al., 1977a, b, 1978a, b; Bell et al., 1978) led to the recognition that TAs are the principal allelochemicals involved in the species' defense mechanism against herbivory. The TAs such as gossypol, heliocides ([H.sub.1], [H.sub.2], [H.sub.3], and [H.sub.4]) and hemigossypolone (HGQ) have been bioassayed for activity against Heliothis virescens F. and other insect pests in artificial diets (Stipanovic et al., 1977a; Chan et al., 1978; Hedin et al., 1981). The heliocides and gossypol retard growth of H. virescens about equally, while HGQ is slightly less effective (Stipanovic et al., 1990). Glandless cotton genotypes devoid of "gossypol glands" are extremely susceptible to herbivorous pests (Bottger et al., 1964; Jenkins et al., 1966), while resistance to insects is enhanced when TAs are genetically increased in the foliage (Williams et al., 1987). Of 56 accessions of G. hirsutum L. resistant to Heliothis spp., 33 were high in TAs (Jenkins, 1995).

High-performance liquid chromatography is an effective technique for detecting and quantifying individual TAs (Greenblatt and Stipanovic 1984; Mahoney and Chan 1985; Stipanovic et al., 1988). Results with this technique have shown that gossypol is the dominant TA in cotton seed but not in the foliar glands. Hemigossypolone and the heliocides constitute up to 90% or more of the total TAs in leaves and up to 45% in flower buds (Altman et al., 1989; Stipanovic et al., 1988). Benson et al. (1995) analyzed seven genotypes of G. hirsutum for TAs using HPLC and found a high level of heliocides [H.sub.1] and [H.sub.4] in the carpel wall compared with the leaves. HPLC analysis of the seeds of Gossypium species in sections Sturtia (R. Brown) Tod. and Hibiscoidea Tod. did not show detectable amounts of TAs, but seeds of species in section Grandicalyx Fryxell had gossypol (Brubaker et al., 1996).

Most work on the TAs of Gossypium species has been limited to the seed, but the available data clearly show that the foliar TAs differ from the TAs in seed. We undertook this study to obtain additional information on the TAs in the leaves of Gossypium species. The foliar quality and quantity of seven selected TAs were determined for 40 Gossypium genotypes including 30 species, several of which have not been previously analyzed. This information will assist in the identification of germplasm that may be used to modify cotton on the basis of qualitative and quantitative enhancement of TAs.

MATERIALS AND METHODS

Forty-one genotypes were included in the TA survey. Represented were 30 species of Gossypium comprising A, B, C, D, F, G, K, and AD genomic groups, and Thespesia thespesioides (Table 1), a genus in the Gossypieae tribe which, like Gossypium, has lysigenous foliar glands. The size and enormous diversity among the species and genomes of Gossypium in morphology, growth habit, and preferred ecological niche makes it difficult to establish and maintain multiple accessions of each species under the same environments. Because of the limits of our facilities, this initial survey was designed to obtain a broad representation of the diversity within the genus from a limited number of accessions of each species, usually only one. Because accession, plant age, and environment may contribute to apparent diversity, efforts were made to minimize some of the non-genetic variability. This included maintenance in pots in a common greenhouse where temperatures ranged between 20 [degrees] C minimum at night and 40 [degrees] C maximum during the day. The plants were watered as needed and fertilized once a week with Peters complete fertilizer (Scotts Company, Marysville, OH). All plants were at least a year old and some of the arborescent species were more than 10 yr old.

Table 1. Foliar terpenoid percent and concentrations (mg [kg.sup.-1] of dry leaf tissue) in Gossypium species and Thespesia thespesoides.
                                   HGQ([dagger])        G

Species                   Genome     %     mg/kg     %    mg/kg

G. herbaceum A1-125        A1        0       0       0       0
   herbaceum africanum     A1        1      12     6.1      72
   arboreum A1-9820        A2      0.6      13     0         0
   anomalum                B1      1.9     231     0.3      42
   capitis-viridis         B3      0.7      92     0.8      99
   longicalyx              F1     30.3   1 162     4       153
   sturtianum              C1      2.8      91     0.8      27
   robinsonii              C2        7     454     4.7     304
   bickii                  G1     27.1     243     0         0
   australe                (G2)   21.7     908     2.5     105
   nelsonii                (G3)    2.4     109     0.3      12
   pilosum                 K      63.1     701      23      26
   enthyle                 K      22.2     261     0         0
   rotundifolium 499790    K       1.1      15     3.6      49
   rotundifolium 499789    K       0        0      0.9      14
   populifolium            K       3.4      47     0         0
   pulchellum              K      63.4     981     2.8      44
   nobile                  K      14.8   1 314     5.2     463
   thurberi                D1      0         0    100       517
   armourianum             D2-1    8.1      21    69.7     182
   harknessii              D2-2   20.9     108    67.7     350
   turneri                 D10     0         0   100       777
   davidsonii              D3-d    0.9      30    99.1   3 374
   schwendimanii           D12     0         0     3.5      71
   lobatum                 D7      0         0     2.8      93
   aridum                  D4      0         0   100     3 127
   laxum A1                D9      0.3      26    52.7   4 404
   laxum A2                D9      1.2      79    22.3   1 473
   laxum B1                D9      0.4      19     0         0
   laxum B2                D9      0         0     0.5      17
   laxum C1                D9      1.2      52    98.8   4 263
   laxum C2                D9      2        45    98     2 219
   laxum C3                D9     56.4     614    43.6     475
   raimondii (r = 3283)    D5      0       0       2.5      87
   tomentosum              AD3    71.9   1 263     2.1      36
   mustelinum              AD4     7.6   1 144     3.9     590
   hirsutum T-2096         AD1     3.7     195     3.2     169
   hirsutum cms-D8 818     AD1     4.2      64     6.6     100
   hirsutum Ark-818        AD1     8.9     210     1.2      29
   barbadense 57-4         AD2    38.4     138     0         0
T. thespesiodes             -      5.7     439    92     7 060

                               [H.sub.1]      [H.sub.2]

Species                       %     mg/kg     %    mg/kg

G. herbaceum A1-125        100        104    0         0
   herbaceum africanum      66.6      789   10.6     126
   arboreum A1-9820          8.8      187   66.4   1 412
   anomalum                  1.3      158   73.8   9 038
   capitis-viridis           0.9      107   74.6   9 267
   longicalyx               36.4    1 398    9.4     359
   sturtianum               73.8    2 396    9.8     317
   robinsonii               40.7    2 634   25.7   1 664
   bickii                   50.7      455    9.5      85
   australe                 27.5    1 153   27.8   1 164
   nelsonii                 26      1 179   47     2 132
   pilosum                  8.9        99    14.4     160
   enthyle                  28.4      333   30.2     354
   rotundifolium 499790     66.5      904   14.2     193
   rotundifolium 499789     58.1      885   17.1     261
   populifolium             50.3      692   21.2     292
   pulchellum                3.6       55   17.8     276
   nobile                   26.5    2 353   38.7   2 552
   thurberi                  0          0    0         0
   armourianum              22.2       58    0         0
   harknessii               11.4       59    0         0
   turneri                   0          0    0         0
   davidsonii                0          0    0         0
   schwendimanii             7        142   40.2     819
   lobatum                  11.5      381    0         0
   aridum                    0          0    0         0
   laxum A1                 12      1 004   21.3   1 782
   laxum A2                 20      1 316   47.6   3 141
   laxum B1                 36.7    1 743   63     2 997
   laxum B2                  4        149   94     3 501
   laxum C1                  0          0    0         0
   laxum C2                  0          0    0         0
   laxum C3                  0          0    0         0
   raimondii (r = 3283)      1.6       56    0         0
   tomentosum               15.1      266    0         0
   mustelinum               29.6    4 457   30.1   4 533
   hirsutum T-2096           5.3      281   67.8   3 590
   hirsutum cms-D8 818      12.2      185   54.6     832
   hirsutum Ark-818         15        357   51.1   1 214
   barbadense 57-4          43.5      156    0         0
T. thespesiodes              1.6      120    0.8      63

                               [H.sub.3]        [H.sub.4]    TTA

Species                        %    mg/kg      %    mg/kg   mg/kg

G. herbaceum A1-125           0         0     0         0      104
   herbaceum africanum        0         0    15.6     185    1 184
   arboreum A1-9820          20.7     441     3.4      73    2 126
   anomalum                  22.3   2 728     0.4      53   12 250
   capitis-viridis           22.6   2 811     0.4      54   12 430
   longicalyx                13.4     515     6.6     253    3 840
   sturtianum                 0         0    12.9     418    3 249
   robinsonii                17.1   1 105     4.8     306    6 467
   bickii                     0         0    12.7     114      897
   australe                  17       711     3.5     145    4 188
   nelsonii                  20       906     4.3     195    4 533
   pilosum                    5        55    63        70    1 111
   enthyle                   12.4     146     6.8      80    1 174
   rotundifolium 499790       9.3     126     5.4      73    1 360
   rotundifolium 499789      15.2     231     8.7     133    1 524
   populifolium              17.5     241     7.6     104    1 376
   pulchellum                 5.6      87     6.7     104    1 547
   nobile                    19.5   1 735     5.3     473    8 890
   thurberi                   0         0     0         0      517
   armourianum                0         0     0         0      261
   harknessii                 0         0     0         0      517
   turneri                    0         0     0         0      777
   davidsonii                 0         0     0         0    3 404
   schwendimanii             49.4   1 007     0         0    2 039
   lobatum                   85.7   2 828     0         0    3 302
   aridum                     0         0     0         0    3 127
   laxum A1                   0         0    13.6   1 134    8 350
   laxum A2                   0         0     8.9     585    6 594
   laxum B1                   0         0     0         0    4 759
   laxum B2                   0         0     1.6      58    3 725
   laxum C1                   0         0     0         0    4 315
   laxum C2                   0         0     0         0    2 264
   laxum C3                   0         0     0         0    1 089
   raimondii (r = 3283)       0         0     0         0    3 426
   tomentosum                73       128     0        64    1 757
   mustelinum                18     2 718    10.8   1 629   15 071
   hirsutum T-2096           18.5     982     1.5      81    5 298
   hirsutum cms-D8 818       17.8     271     4.7      71    1 523
   hirsutum Ark-818          18       427     5.8     137    2 374
   barbadense 57-4            0        0     18.1      65      359
T. thespesiodes               0        0      0         0    7 682


([dagger]) HGQ = hemigossypolone; G = gossypol; R = raimondal (in G. raimondii); [H.sub.1], [H.sub.2], [H.sub.3] & [H.sub.4] = Heliocides; TTA = Total terpenoid aldehydes.

Leaves at Nodes 8 to 10 below terminals were selected from all species as representative of a similar, mature growth stage since all the species are perennials with cyclical growth. All samples were washed, blotted dry, frozen at -80 [degrees] C, freeze-dried, and ground with a Wiley mill to pass a 20-mesh screen.

The HPLC procedure outlined by Stipanovic et al. (1988) was used for analyses of TAs. Samples of ground leaves (100 mg) were shaken (225 rpm) for 30 min in a capped 125-mL Erlenmeyer flask with 15 mL of glass beads, 10 mL of 3:1 hexane:ethyl acetate (HEA), and 200 mL of 10% (v/v) HCl. The solution was filtered through Whatman No. 1 filter paper supported on a fritted filter disk into a 50-mL pear-shaped flask, and the beads and residue were rinsed three times with 2 to 3 mL of HEA. The solvent was evaporated with an air stream, the residue in the flask redissolved with HEA (4 x 150 mL), and each wash transferred to a Maxi-clean silica cartridge (Alltech). The silica cartridge was dried with a stream of N2 gas, and then terpenoid compounds were eluted with 5 mL of isopropyl alcohol (IPA), acetonitrile (ACN), water, and ethyl acetate (EtOAc) (35:21:39:5). The eluent was filtered through a 0.22-[micro]m nylon membrane (MSI), and a 1 mL aliquot was transferred to a vial and sealed. The samples were analyzed soon after extraction because they were found to degrade with time.

Samples were analyzed on a Water HPLC system (Water Corp., Milford, MA), equipped with a Water Model 490 programmable multiwavelength detector and a Spectra Physics Model 4100 integrator (Spectra-Physics AB, Stockholm), using a 15-cm x 3.9-mm Novapak C-18 column (Novapak Corp., Philmont, NY). The mobile phase was ethanol, methanol, IPA, ACN, [H.sub.2]O, EtOAc, dimethylformamide, and phosphoric acid (16.7:4.6:12.1:20.2:37.4: 3.8:5.1:0.1) at a flow rate of 5 mL [min.sup.-1]. Peak detection was at 272 nm. Duplicate 20 [micro]L injections were made of all samples. Standard curves for G, HGQ, [H.sub.1], [H.sub.2], and R (Fig. 1) were constructed from the average of three replications each at concentrations of 5, 10, 25, and 50 [micro]g [mL.sup.-1] Standard curves for [H.sub.1] and [H.sub.2] were used to quantify [H.sub.4] and 1-13, respectively, and the results were expressed as mg TA [kg.sup.-1] of dry tissue. Also, within an accession individual TAs were expressed as percentage of the total TAs to obtain an indication of relative abundance of each TA for the accession.

[Figure 1 ILLUSTRATION OMITTED]

RESULTS AND DISCUSSION

This report constitutes a broad survey intended to provide an estimate of the genetic diversity in selected TAs within the Gossypium genus. We recognize that different accessions within a species, environmental factors, and age of the plant may differentially influence synthesis and accumulation of TAs. We attempted to minimize non-genetic variability by growing all the plants in pots in a greenhouse, and harvesting leaves from the same developmental position on the stem during the summer months. However, the values for specific concentrations and percentages of TA of the various accessions should not be considered absolute, but they should be roughly representative of the diversity present among the species. Extremes in TA concentration, for example the absence of a specific TA, probably are accurate representations of the species in which they Occur.

Two features are important when comparing the TAs among the various Gossypium species and accessions. The first is the concentration of each TA per unit of tissue, and the second is the percentage of total TAs in the tissue attributable to each specific TA. The first value is related to gland size and density in the leaf tissue, parameters that are primarily genetically fixed. Concentration may be influenced by environment also. For example, total concentration of TA varied 100% among locations in Texas (Stipanovic et al., 1988). The second parameter is related to differential genetic regulation among the species of the biosynthetic pathways leading to the various TAs. Again, influence of environment on the various branch pathways that would differentially change the relative concentration of the various TAs is not well known, although Stipanovic et al. (1988) reported that HGQ fluctuated the most across environments. While the results would be expected to differ across environments, the current results provide an adequate comparison among accessions because of their common root (potting medium) and greenhouse environment and management practices.

The species with the highest total TA were G. mustelihum Miers ex Watt, G. capitis-viridis Mauer, and G. anomalum Wawra ex Wawra & Peyritch, each with TA in excess of 1.2 g [kg.sup.-1] of dry leaf tissue. Table 2 identifies the Gossypium species with the highest quantity and the species with the highest percentage of total for each of the individual TAs. Among the species examined, the species with the highest quantity of a specific TA usually was not the species with the highest percentage of that TA. For example, G. mustelinum had the highest concentration of two of the heliocides, but it was not the species with the highest percentage of total for either of these. For three of the species, gossypol was the only TA in the leaves, so in this case they each had a percentage of 100. Those species with high percentage values for individual TAs were extremes in all cases except for [H.sub.3], which appears to be a minor component in Gossypium.
Table 2. Species of Gossypium with highest quantity and percentage
of each terpenoid aldehyde.

                   Species with                 Species with
TA               highest quantity             highest percentage

HGQ           nobile (K)                    tomentosum ([AD.sub.3])
Gossypol      laxum (D)                     thurberi (D)
                                            turneri (D)
                                            aridum (D)
[H.sub.1]     mustelinum ([AD.sub.4])       herbaceum ([A.sub.1])
[H.sub.2]     capitis-viridis ([B.sub.3])   laxum ([D.sub.9])
[H.sub.3]     lobatum ([D.sub.7])           Iobatum ([D.sub.7])
[H.sub.4]     mustelinum ([AD.sub.4])       barbadense ([AD.sub.2])


The total concentration of TAs and the percentage represented by HGQ, gossypol, and [H.sub.1] to [H.sub.4] in the leaves of each genotype are given in Table 1. This is the first report on the evaluation of the terpenoid aldehydes in the leaves of T. thespesioides and in many of the species in the B, C, D, F, G and K genomic groups of Gossypium.

Prior to these analyses, we considered the possibility that significant qualitative differences in TA accumulation might emerge that would distinguish the different genomic groups. This did not occur. The differences in patterns of TA accumulation among species within a genomic group made comparisons between genomes meaningless (data not shown).

Gossypium mustelinum ([AD.sub.4]) was notable for its high concentration of total TAs, of which [H.sub.2] (30.1%) and [H.sub.1] (29.6%) were the dominant contributors, although each of the other TAs, except gossypol (3.9%), were also present in moderately high levels. At the other extreme, an accession of the cultivated diploid G. herbaceum L. (A1-125) contained less than 1% of the TA concentration of G. mustelinum, and that was limited to the single heliocide [H.sub.1]. The other two species of the A-genome group, G. herbaceum ssp. africanum Watt ([A.sub.1]) and G. arboreum L. ([A.sub.2]), while having a relatively low TA concentration, did possess all TAs except [H.sub.3] and gossypol, respectively. Gossypium arboreum A1-98 possessed a higher concentration of total terpenoid aldehydes relative to the other two species. Our results for the A genome are similar to those reported by Altman et al. (1990).

In the B genomic group G. anomalum ([B.sub.1] and G. capitis-viridis ([B.sub.3]) had very similar total TA concentrations and relative abundance of three heliocides, whereas the quantities of the other TAs were more variable (Table 1). Heliocides [H.sub.2] and [H.sub.3] were exceptionally high, thus this group could be a useful source for the selection of enhanced levels of these TAs. The high concentration of TAs was probably related to the exceptionally large lysigenous glands in the leaves of these species. The monospecific F genome (G. longicalyx Hutchinson & Lee) possessed all six TAs but the total TA concentration was only moderate (Table 1). Of these, [H.sub.1] and HGQ were most abundant, while gossypol was present in the lowest quantity.

The C-genome species G. sturtianum Willis ([C.sub.1]) and G. robinsonii Muell. ([C.sub.2]) had only moderate concentrations of TAs, although the amount in the [C.sub.2] accession was twice that of [C.sub.1] (Table 1). [H.sub.1] was the most abundant TA in both species, but the second most abundant TA differed between them, [H.sub.4] and [H.sub.2] respectively. The results of Wendel and Albert (1992) suggest that [C.sub.2] is phylogenetically basal in the genus, thus most like the ancestral type. In this regard, it is interesting that [C.sub.2] possessed all the heliocides as well as gossypol and HGQ, whereas [H.sub.3] was absent in the [C.sub.1] accession examined. This may be a distinguishing feature between the two species and may also have some significance relative to the results observed with G. bickii Prokhanov discussed below.

The relative concentration of gossypol was low in the leaves of G-genome species. Gossypium nelsonii Fryxell and G. australe Muell. possessed almost equal quantities of TA (Table 1). Heliocide [H.sub.2] was high in G. nelsonii, whereas the percentage was intermediate in G. australe, and low in G. bickii. Gossypium bickii had only about 20% of the TA concentration of the other two species, and half of that was [H.sub.1]. The qualitative pattern of TAs in G. bickii was more similar to that of [C.sub.1] than the other G-genome species, with [H.sub.3] being absent in both species. However, the high percentage of HGQ in G. bickii is a feature shared with G. australe. The intermediate nature of G. bickii may be attributable to its ancestral hybrid origin (Wendel et al., 1991; Wajahatullah and Stewart, 1997).

A consistent qualitative pattern of TA was not evident in the species of the K genome except that gossypol was the lowest foliar TA (Table 1). The qualitative patterns did suggest species pairs, for example G. pilosum Fryxell and G. pulchellum (Gardner) Fryxell, G. enthyle Fryxell, Craven & Stewart and G. nobile Fryxell, Craven & Stewart, and G. rotundifolium Fryxell, Craven & Stewart and G. populifolium (Benth.) Muell. ex Tod. Gossypium nobile was notable in that it possessed three times more TAs than other species in this group, and it had significant quantities of all six of the TAs with heliocides [H.sub.1] and [H.sub.2] predominating.

Among the species of Australia (C, G and K genomes), [H.sub.1] was the most abundant heliocide followed by [H.sub.2] (Table 1). Exceptions to this generalization were G. nelsonii, which possessed more [H.sub.2], and G. pilosum and G. pulchellum which had 63% of their TAs as HGQ. Brubaker et al. (1996) did not find gossypol in mature embryos of the C- or G-genome species, either visibly (glands) or analytically, but they found a significant amount of gossypol in the seeds of K-genome species. Our results showed higher levels of total TAs on average in the leaves of C- and G-genomic species compared with the K-genome species (Table 1). The negative correlation between the TA levels of the seed and leaves of the C- and G-genome species has received considerable attention as a genetic source for glandless seed while maintaining significant amounts of foliar TAs (Stewart, 1995).

From the perspective of individual TAs, the D genome was most variable (Table 1). As previously reported by Altman et al. (1990), gossypol was the predominant TA in the D genome with the exception of a few species. Interestingly, the species endemic to northwestern Mexico [G. thurberi Tod., G. turneri Fryxell, G. harknessii Brandegee, G. armourianum Kearney, G. davidsonii Kellogg, and G. aridum (Rose & Standley) Skovsted in part] had very little heliocide in their leaves. In these species gossypol was the dominant foliar TA, and in the leaves of G. thurberi, G. turneri, and G. aridum gossypol constituted the entire TA content. In as much as three different taxonomic sections are involved, ecological convergence is suggested.

Our results with G. laxum indicate that this species, as currently circumscribed, is highly variable among accessions in both quality and quantity of TA (Table 1). The initial G. laxum accession tested gave the highest total TAs among the D-genome species, consequently, several other accessions were tested. Surprisingly, three different qualitative patterns were obtained for individual TAs. One group had high quantities of gossypol, [H.sub.1] and [H.sub.2], a second group had abundant [H.sub.1] and [H.sub.2], and a third group had no heliocides but were high in gossypol. One accession had the highest absolute amount of gossypol in the genus, however another accession possessed 94% of its TAs as [H.sub.2]. Based on these results, the classification of these accessions should be examined closely.

The D-genome species exhibited no consistent qualitative pattern for the TAs that distinguished it from other genomes (Table 1). For each generalization there were exceptions. For example, none of the species possessed [H.sub.3] except G. schwendimanii Fryxell & Koch and G. lobatum. The G. lobatum accession had both the highest amount and the highest relative content (85.7%) of [H.sub.3]. Also, [H.sub.4] was absent in the D genome except for three accessions of G. laxum. As others have reported (Stipanovic et al., 1980; Altman et al., 1990, 1991; Khan et al., 1993), G. raimondii possessed the unique TA, raimondal (relative content of 95.8%), and low concentrations of gossypol and [H.sub.1].

In the AD genome, all six TAs were present (Table 1). [H.sub.2] was the predominant TA in G. hirsutum and G. mustelinum accessions, whereas [H.sub.1] and HGQ predominated in G. barbadense L. and G. tomentosum Nutall ex Seemann, respectively. Leaf gossypol was in relatively low quantity within the entire AD genome. Gossypium mustelinum had more total TA than any other Gossypium species. Except for gossypol, foliar concentration of each TA was high in this species. The presence of all terpenoids in the AD genome may be due to the contributions from both the A- and D-genome, ancestral parents, a conclusion also reached by Altman et al. (1990). The species within the AD genome could be utilized for the introgression of total TA through intra- and interspecific breeding to enhance pest resistance in cotton cultivars.

Like Altman et al. (1991), we observed that some species had several unknown compounds. Most of the species with lower quantities of the six common TAs usually had higher quantities of unknown compounds (Fig. 2). Some of these compounds might be terpenoids that confer unique resistance, so further analyses should be made to characterize these compounds.

[Figure 2 ILLUSTRATION OMITTED]

One of the characteristics of the genera in the Gossypieae tribe is the presence of lysigenous glands presumed to sequester TAs. Although Gossypium is well characterized, other genera are not. Our analysis of T. thespesioides revealed that 92% of the TAs sequestered in the leaves is gossypol. The concentration was nearly twice that of the Gossypium species that accumulate primarily gossypol (e.g., G. davidsonii, G. laxum, G. turneri, etc.). Minor quantities of [H.sub.1], [H.sub.2] and HGQ were also present in T. thespesioides.

Recently, molecular biologists have combined HPR and biological insecticides into genetic engineering of crops that continuously produce insecticidal or antinutritive proteins for insect pest control. Further work involving molecular techniques could provide for more efficient evaluation and introgression of TAs into economic genotypes with specific molecular markers. The ability of Heliothis spp. to develop resistance to chemical and bioengineered insecticides, and the increasing environmental concerns resulting from the use of chemical insecticides for their control emphasize the need for the introduction of alternative methods of managing these pests. These analyses reveal a wide diversity among Gossypium species in the quality and quantity of TAs sequestered in the leaves. These species provide opportunity for the selection of species-specific individual terpenoids. The selected species should be a good source for enhancement of HPR based on broad TA contents. Several species are identified that could be useful tools in the elucidation of specific biosynthetic pathways because of their limited diversity in TAs. Also, it is apparent that additional compounds exist, but any role in HPR is totally unknown.

ACKNOWLEDGMENTS

We are grateful to Dr. R.D. Stipanovic for providing the gift of standards.

Abbreviations: [H.sub.1], heliocide 1; [H.sub.2], heliocide 2; [H.sub.3], heliocide 3; [H.sub.4], heliocide 4; HGQ, hemigossypolone; HPLC, high performance liquid chromatography; HPR, host-plant resistance; TA, terpenoid aldehyde.

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M. Altaf Khan, J. McD. Stewart,(*) and J. B. Murphy

M.K. Altaf and J.McD. Stewart, Agronomy Dep.; J.B. Murphy, Horticulture Dep., Univ. of Arkansas, Fayetteville, AR 72701. Contribution of the Arkansas Agric. Exp. Stn. Received 3 Nov. 1997. (*)Corresponding author (jstewart@comp.uark.edu).
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