Abstract
The large genetic evolution due to the sexual reproduction-mediated gene assortments and propensities has made Venturia inaequalis (causing apple scab) unique with respect to its management strategies. The resistance in apple germplasm against the scab, being controlled for by more than fifteen genes, has limited gene alteration-based investigations. Therefore, a biological approach of bacterial endophyte community dynamics was envisioned across the apple germplasm in context to the fungistatic behavior against V. inaequalis. A total of 155 colonies of bacterial endophytes were isolated from various plant parts of the apple, comprising 19 varieties, and after screening for antifungal behavior followed by morphological, ARDRA, and sequence analysis, a total of 71 isolates were selected for this study. The alpha diversity indices were seen to fluctuate greatly among the isolation samples in context to microflora with antifungal behavior. As all the isolates were screened for the presence of various metabolites and some relevant genes that directly or indirectly influence the fungistatic behavior of the isolated microflora, a huge variation among the isolated microflora was observed. The outstanding isolates showing highest percentage growth inhibition of V. inaequalis were exploited to raise a bio-formulation, which was tested against the scab prevalence in eight apple varieties under controlled growth conditions. The formulation at all the concentrations caused considerable reductions in both the disease severity and disease incidence in all the tested apple varieties. Red Delicious being most important cultivar of the northwestern Himalayas was further investigated for its biochemical behavior in formulation and the investigation revealed different levels of enzyme production, chlorophyll, and sugars against the non-inoculated control.
Highlights
Apple (Malus domestica Borkh) belongs to the plant family Rosaceae, which is comprised of more than 100 genera and 300 species across the world, most frequently established in temperate climates [1]
We found that the highest number of fungistatic bacterial strains were isolated from Golden Delicious germplasm, followed by Fenna, and lowest number derived from the variety Fuji Zehn Aztech and Gala Mast, giving an indication to the existence of heterogeneity among the sampled cultivars in the context of scab resistance
The present study revealed that there is an abundant diversity of bacterial microflora across the Himalayan apple germplasm with respect to their antifungal behavior against V. inaequalis
Summary
Apple (Malus domestica Borkh) belongs to the plant family Rosaceae, which is comprised of more than 100 genera and 300 species across the world, most frequently established in temperate climates [1]. The area in Jammu and Kashmir utilizes 136.54 thousand hectares for its apple production. 12.50 tons per hectare [2,3] Several fungal pathogens such as Venturia inequalis, Podosphaera leucotrichia, Alternaria mali, etc., cause a huge loss to the apple industry. Wint causing apple scab is economically the most significant pathogen. In the Jammu and Kashmir state, this disease was reported in 1970s and ever since, it has caused havoc in the apple industry with the extent of fruit loss of up to 60%, estimating an amount in hundreds of crores [4]. When an ascospore lands on a susceptible leaf or fruit, it form lesions, leading to the formation of mitospores (conidia), which are splashed by water or blown by wind to bring the secondary infection. Systemic fungicide sprays limited to seven in number have previously been able to contain the disease but due to the emergence of fungicide resistance in pathogens, these practices have become obsolete [6]
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