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GEOSTATISTICAL ANALYSIS OF TOMATO FRUIT ROT AND DIVERSITY OF ASSOCIATED FUNGAL SPECIES.

Byline: A. Hussain, S. W. Khan, S. Ali, F. Faiz, M. Hussain, A. Ali, Shams Ur Rahman and S. Qasim

Key words: Tomato rot, distribution, GIS, geostatistics, associated fungi, Gilgit-Baltistan

INTRODUCTION

Postharvest diseases of fruits and vegetables may occur at the time of harvesting to consumption that make food commodity toxic and reduce aesthetic value due to alterations in appearance, texture, taste or smell (Akinmusire, 2011). Tomato (Solanum lycopersicum L.) which belongs to the family Solanaceae is an important vegetable crop grown throughout the World. It is considered as highly nutritious due to its high contents of vitamin A and C as well as lycopene; a natural antioxidant. It has niacin 0.712 mg, calcium 31 mg and water 94.28g per 100g weight (Wamache, 2005; Ewulo et al., 2008). It is the 2nd most consumed vegetable next to potato and ranked first among the processing crops. It is the most popular and key vegetable grown in the entire world and significantly contributes to the world's vegetable economy (FAOSTAT, 2019; Quinet et al., 2019; FAO, 2005).

In the developing countries tomato fruits are displayed in baskets at the open markets, thereby exposing them to opportunistic microbial infections especially mycotoxins producing organisms. Microbial contamination of fruits and vegetables may occur during harvesting, storage, packaging and transportation (Baiyewu et al., 2007; Barth et al., 2009). The poor postharvest handling practices in the developing countries amounting to approximate losses >30% of fresh fruits and vegetables (Kader, 2005; Agrios, 2005). Like other crops; a huge amount of tomato crops is lost after harvest. The main factors of post-harvest losses are; careless harvesting, dumping of produce, improper storage, bulk packaging and transportation to the distant markets. All these activities increase moisture condensation which supports pathogen infestation and decay of produce.

Due to perishable nature of tomato fruits; postharvest decay remains a major challenge to the grower (Mujib et al., 2007). There are numerous microorganisms including fungi, bacteria, viruses and nematodes that cause different diseases of tomatoes. Amongst; fungi are mainly responsible for causing serious threats to the quality of tomato fruit. Furthermore, high contents of moisture make tomato fruit more prone to fungal contamination (Efiuvwevwere, 2000; Kalyoncu et al., 2005; Wani, 2011).

Several fungi caused rots reported all over the world having varying intensities on tomato (Iqbal et al., 2003; Patel et al., 2005; Ali et al., 2005). Adequate information about microbial contamination and handling practices could lessen postharvest wastage of fruits. Tomato fruit having high water contents (80%), rich nutrient, sugar as well as low pH, serves as an excellent environment for microbial contamination (Singh and Sharma, 2007). Farmer and tomato seller of Gilgit-Baltistan are faced with serious losses due to attack of microbes especially by rot pathogens. The losses may start from field and continue to sale at the market. Knowledge of microbial contamination of tomato fruits is necessary to developed postharvest management strategies with specific treatment before reaching to consumer to avoid adverse human health and financial impacts.

Spatial distribution of plant disease by using GIS has identified the areas where infestation is high and it helps in devising effective management strategies (Richard et al., 2005). In this study; the spatial distribution of tomato rot and associated fungus was assessed using descriptive and geostatistical software. The study also used semivariogram analysis to narrate the spatial pattern and generate tomato rot probability maps by using kriging techniques. This study also addresses abundance and diversity index of associated fungal species.

MATERIALS AND METHODS

Spatial distribution of tomato rot: To assess spatial distribution of tomato rot (incidence and severity); tomato fruits showing rotting symptom were collected from different fields, shops/ markets in the selected valleys of districts Gilgit (Fig. 1). A total of fifty tomato fruits were randomly collected from each point and calculated incidence and severity by using following formula:

T.R.I% = N.T.R.T/T.N.T.Ix100

T.R.I% = Tomato rot incidence percentage; N.T.R.I = Number of tomato rot infected; T.N.T.I = Total number of tomatoes inspected

Tomato rot severity was determined according to scale (a$? 3 mm; 3-5 mm and [greater than or equal to] 6 mm rot length). The rot severity index percentage was calculated by using following formula;

D.S.I = IPS A.R/T.N.R (M.D) x100

(D.S.I = Disease severity index; IPSA. R = Sum of all disease rating; T.N.R = Total number of rating; M. D= Maximum disease grade.

Geostatistical analysis and Spatial Variability Mapping of tomato Rot: Geostatistical analysis was used to describe the spatial distribution of tomato rot in term of incidence and severity. ArcGIS 10.1 and ArcGIS Geostatistical Analyst were used for mapping of disease. Kriging technique was used to interpolate the values of unsampled locations as described by Caers, 2003. The following formula was used for kriging;

Z(SO)= IPSN i=1 I>>i Z(Si)

Where: Z(si) = the measured value at the ith location; I>>i = an unknown weight for the measured value at the ith location; s0 = the prediction location; N = the number of measured values.

Semivariogram can be fitted with spherical model presented by Olea 2003; Webster and Oliver, 2007. Spherical = y(h) = {C0 + C (3h/2ac - A1/2(h/a)3

0 a$? h < a

h [greater than or equal to] a

Spatial dependence (SDP%) was calculated as described by Biondi et al. (1994), is given by the expression;

SDP Spherical% = C1 /C0 + C1x 100

For the spherical semivariogram: SDP Spherical (%) was taken as; a$? 25% weak spatial dependence; 25% 10% can be considered the first indicator of heterogeneity of data or presence of diseased plants in different locations.

In the current investigation; nine different fungal species were isolated from infected tomatoes which caused significant postharvest losses in the study area. It has been established that fruit rot of tomato is commonly triggered by different opportunistic fungal pathogens. These pathogens are widespread in the environment. Mechanical injuries during harvesting and handling provide room for infection and subsequent fruits decay by the pathogens. Fruit decay is activated with the change in physiological state of fruits, which may further enhance due to poor handling, storage and transportation practices (Wilson et al., 1991). Additional factors like low pH, higher moisture level and nutrient composition make fruits very susceptible to pathogenic fungi. In addition to causing rots; these pathogens also produce mycotoxins (Moss, 2002). The results obtained from the current study indicated that nine fungi were associated with tomato fruits with different occurrence percentage.

Similar rotting fungal species were also recovered from tomato fruit by Muhammad et al., (2004). These results agree with those of Chuku et al. (2010) who reported that Fusarium spp. R. stolonifer and Aspergillus spp. were responsible for soft rot of tomato. Ijato et al. (2011) isolated A. niger, F. oxysporum, R. stolonifer and G. candidium from rotten tomato fruits. F. moniliforme, A. niger and R. stolonifer were isolated from rotten tomato fruits (Chuku et al., 2008). The decay of fruits during storage is due to the micro-organisms which could have gained entry through cracks and surface injuries (Onuoral and Orji, 2015). According to Kader (2002), the pathogens infect fruits during prolonged periods of rainfall and high humidity, especially when fruits are poorly packed. The consequences of microbial contamination on tomato fruits causes spoilage, lessened sensory appeal and shelf life leading to loss and wastage of product that have significant economic cost.

The microbiological safety of these products has also become a significant issue; as the incidence of food borne disease outbreaks are associated with their consumption (Obunukwu et al., 2018). Based on the information of current research work; It is suggested that intake of contaminated tomato's should be avoided. Mitigation measures must be employed by tomato growers, marketers and consumers at the time of harvesting, transportation, handling, storage and processing of tomato fruits.

Conclusion: This study discloses that tomato fruit rot is spatially distributed and massively infected with different fungal species. A total of nine fungal species were isolated from tomato fruits. Amongst; the highest occurrence percentage was in Aspergillus flavus followed by Fusarium oxysporum and Alternaria alternata. The high prevalence of tomato rot fungi necessitates appropriate management strategies. Adequate pre-post practices of produce would be fruitful to minimize wastes and enhance sustainable livelihood options. The current endeavor refers the effective role of GIS for highlighting as well as easily understanding of agriculture problems through thematic maps. Spatial distribution mapping and geostatistical analysis will be useful for researchers, extension worker and farmers in selection of cultivars and develop appropriate post-harvest practices for managing better crop and income.

Acknowledgments: The authors are grateful to Karakorum International University Gilgit, Gilgit-Baltistan for providing the financial assistance to carry out this research work.

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Author:A. Hussain, S. W. Khan, S. Ali, F. Faiz, M. Hussain, A. Ali, Shams Ur Rahman and S. Qasim
Publication:Journal of Animal and Plant Sciences
Geographic Code:6NIGR
Date:Jun 22, 2021
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