ABSTRACT
Pomegranate bacterial blight caused by Xanthomonas axonopodis pv. punicae (Xap) is a highly destructive disease. In the absence of host resistance to the disease, we aimed to evaluate the biocontrol potential of endophytic bacteria against Xap. Thus, in this study, we isolated endophytes from pomegranate plants, identified them on the basis of 16S rDNA sequencing, tested them against Xap, and estimated the endophyte-mediated host defense response. The population of isolated endophytes ranged from 3 × 106 to 8 × 107 CFU/g tissue. Furthermore, 26 isolates were evaluated for their biocontrol activity against Xap, and all the tested isolates significantly reduced the in vitro growth of Xap (15.65% ± 1.25% to 56.35% ± 2.66%) as compared to control. These isolates could reduce fuscan, an uncharacterized factor of Xap involved in its aggressiveness. Lower blight incidence (11.6%) and severity (6.1%) were recorded in plants sprayed with endophytes 8 days ahead of Xap spray (Set-III) as compared to control plants which were not exposed to endophytes (77.33 and 50%, respectively%) during in vivo evaluation. Moreover, significantly high phenolic and chlorophyll contents were estimated in endophyte-treated plants as compared to control. The promising isolates mostly belonged to the genera Bacillus, Burkholderia, and Lysinibacillus, and they were deposited to the National Agriculturally Important Microbial Culture Collection, India.
ABSTRACT
The present study investigates the genetic diversity and population structure among 42 diverse pomegranate genotypes using a set of twenty one class I hypervariable SSR markers (> 24 bp), which were reported earlier from the analysis of cv. Dabenzi genome. The study material comprised 16 indigenous and 13 exotic cultivars, and 13 wild accessions. A total of 66 alleles (Na) were detected with an average of 3.14 alleles per marker. The average values of polymorphic information content (PIC), observed heterozygosity (Ho) and Shannon's gene diversity index (I) were 0.44, 0.21 and 0.95, respectively suggesting moderate genetic diversity. The pairwise genetic distance ranged from 0.07 to 0.80 with a mean value of 0.53. Population structure analysis divided all the genotypes into four subpopulations (SP1, SP2, SP3 and SP4). Interestingly, the results of phylogenetic and principal component analyses coincided with the results of structure analysis and the grouping of genotypes followed the geographical origins. AMOVA revealed that 25% of the variation was attributed to differences among populations, whereas 75% within the subpopulations with significant F ST value 0.25 (p < 0.001), indicating a high level of genetic differentiations or low level of gene flow. Based on the F ST values, pomegranate genotypes belonging to SP4 (indigenous cultivars) followed by SP1 (exotic lines) exhibited higher gene diversity and genetic differentiations within and among populations. These genetic relationships based on SSR markers could be harnessed in future genetic improvement of pomegranate through informed hybridization programs.
