Abstract
Asian pear scab is a fungal disease caused by Venturia nashicola. The identification of genes conferring scab resistance could facilitate the breeding of disease-resistant cultivars. Therefore, the present study aimed to identify a scab-resistance gene using an interspecific hybrid population ((Pyrus pyrifolia × P. communis) × P. pyrifolia). Artificial inoculation of V. nashicola was carried out for two years. The segregation ratio (1:1) of resistant to susceptible individuals indicated that resistance to V. nashicola was inherited from P. communis and controlled by a single dominant gene. Based on two years phenotypic data with the Kruskal–Wallis test and interval mapping, 12 common markers were significantly associated with scab resistance. A novel scab resistance gene, Rvn3, was mapped in linkage group 6 of the interspecific hybrid pear, and co-linearity between Rvn3 and one of the apple scab resistance genes, Rvi14, was confirmed. Notably, an insertion in pseudo-chromosome 6 of the interspecific hybrid cultivar showed homology with apple scab resistance genes. Hence, the newly discovered Rvn3 was considered an ortholog of the apple scab resistance gene. Since the mapping population used in the present study is a pseudo-BC1 population, pyramiding of multiple resistance genes to pseudo-BC1 could facilitate the breeding of pear cultivars with durable resistance.
Highlights
Venturia species are a threat to stable pear (Pyrus spp.) production; they infect the pear leaves, branches, and fruits leading to defoliation and poor fruit quality
V. nashicola and V. pirina are causes of pear scab [1,2]; V. nashicola only infects Asian pears (P. pyrifolia, P. ussuriensis, and P. bretschneideri), while V. pirina is only pathogenic to European pears (P. communis)
Other studies have shown that multiple resistance (R) genes may be associated with pear scab resistance, and the genetic location of the R gene may differ depending on the resistant host
Summary
Venturia species are a threat to stable pear (Pyrus spp.) production; they infect the pear leaves, branches, and fruits leading to defoliation and poor fruit quality. Cho et al [5] reported Rvn, another R gene to V. nashicola, in LG13 of an interspecific hybrid pear [(P. pyrifolia × P. ussuriensis) × P. communis]. They developed cleaved amplified polymorphic sequence markers linked to the Rvn. Terakami et al [4] suggested a comparison of the genetic location in LG could help understand genome synteny in scab resistance between pear and apple. An interspecific hybrid pear, ‘Greensis’, was selected from seedlings derived from a cross between ‘Whangkeumbae’ (P. pyrifolia) and ‘Bartlett’ (P. communis) [11]. We performed an association mapping study to explore novel R genes, which confer resistance to V. nashicola using a pseudo-BC1 population derived from a cross between scab-resistant ‘Greensis’ [11] and scab-susceptible ‘Whasan’ [13]
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