Population Variation of Apple Scab (Venturia inaequalis) Isolates from Asia and Europe

Abstract

Apple scab, caused by Venturia inaequalis, is one of the most of damaging diseases worldwide on apple and currently is managed mainly by scheduled applications of fungicides. Understanding pathogen population structure is important for breeding and deployment of resistant cultivars. Isolates of V. inaequalis were sampled from a number of cultivars in China, India, and the United Kingdom to estimate differences in pathogen populations. Amplified fragment length polymorphism (AFLP) markers were used to genotype isolates, mostly from China and the United Kingdom. The AFLP data indicated that, overall, there were significant differences in V. inaequalis populations from China and the United Kingdom. Within China, there was no significant differentiation associated with their geographical or cultivar origins. In contrast, populations from four cultivars in two U.K. orchards (monoculture of Gala and a mixture orchard of Bramley, Cox, and Worcester) differed significantly. Furthermore, populations from Gala and Worcester were more homogenous than expected but those from Cox were more diverse than expected. In total, 80 isolates were selected randomly from three countries for virulence testing: 20 from the United Kingdom (10 from Gala and 10 from Cox), 30 from China (10 from Gala, 10 from Fuji, and 10 from Qingquan), and 30 from India (10 from Gala, 10 from Golden Delicious, and 10 from Black Ben Davis); of these 80 isolates, 41, 47, and 59 were inoculated against each of these cultivars in the United Kingdom, India, and China, respectively. The two local cultivars from India (Black Ben Davis) and the United Kingdom (Cox) were more resistant against non-indigenous isolates, particularly those from China, than they were against indigenous isolates; the Chinese local cultivar (Qingguan) showed a higher general level of resistance against isolates regardless of their origin.

Virulence and Molecular Diversity of Venturia inaequalis in Commercial Apple Growing Regions in Kashmir

“…; Xu et al. , ) have observed low genetic differentiation in various V. inaequalis populations and our results confirm these reports.…”

“…Parisi et al (2004) reported 87% European V. inaequalis population to overcome Rvi1, and the present investigation confirms over-dominance of such isolates (>83% isolates) in the valley. The high susceptibility of cultivar Royal Gala and Golden Delicious toward Indian isolates observed in this study is in agreement with that of Xu et al (2008). Few workers have reported the presence of races in different parts of world (Shay and Williams 1956;Heaton et al 1991;Bus et al 2011), and the present report about the presence of these races in Kashmir valley is the first such study from India.…”

“…The result of this study together with previous reports Gessler 1997, 1999;Guerin and Le Cam 2004;Gladieux et al 2008;Xu et al 2008Xu et al , 2012Padder et al 2011) confirms the existence of high variability in V. inaequalis. RAMS and PCR-RFLP profiling of 71 and 69 V. inaequalis isolates of Kashmir in India revealed high levels of diversity without congruence of the phenogram with either the geographical location or the apple cultivars from which isolates were obtained.…”

“…The high susceptibility of cultivar Royal Gala and Golden Delicious toward Indian isolates observed in this study is in agreement with that of Xu et al. (). Few workers have reported the presence of races in different parts of world (Shay and Williams ; Heaton et al.…”

“…Variability in V. inaequalis has been assessed using a standard differential set of cultivars, allowing consistent comparison of data among different research groups for common race spectrum. Many pathotypes (Heaton et al 1991;Parisi et al 1993;Mac Hardy et al 2001;Bus et al 2011) and high level genetic diversity Gessler 1997, 1999;Guerin and Le Cam 2004;Gladieux et al 2008;Xu et al 2008Xu et al , 2012Padder et al 2011) have been reported in V. inaequalis. In our preliminary investigation too, high genetic diversity was observed among the 27 isolates of apple scab fungus (Padder et al 2011).…”