Potential of dioecious progenies of papaya plants for resistance to powdery mildew

ABSTRACT Landraces are important sources of genetic variability to be exploited by plant breeding programs. In Brazil, papaya is commercially grown mainly in the states of Espirito Santo and Bahia but, domestically, it is grown throughout the extensive Brazilian territory. However, exploration studies of genetic variability in local varieties of papaya are incipient in the country. The aim of this study was to evaluate the potential of 20 dioecious papaya genotypes for traits related to resistance to powdery mildew (Streptopodium caricae). Thus, this experiment was conducted in a greenhouse, in randomized block design, with four replicates and one plant per plot. The following were evaluated: incidence of leaves with powdery mildew symptoms and severity of powdery mildew in the fifth and seventh leaves. The obtained data were subjected to analysis of variance and mean comparison test via the least squares method. The variance components and the genetic value of progenies for incidence and severity of powdery mildew were also estimated via mixed models. There was a favorable situation for selection aimed at resistance to powdery mildew, with heritability ranging from 51.57 to 67.82 and selective accuracy above 70%. PMI1, PMI6, PMI8, PMI11, PMI12 and PMI15 stood out for presenting potential to reduce both the incidence and the severity of powdery mildew on foliage.

摘要：地方品种（landrace）是可供植物育种项目利用的重要遗传变异来源。在巴西，番木瓜商业化种植主要集中于圣埃斯皮里图州与巴伊亚州，但在巴西国内，番木瓜种植遍布其广阔领土。然而，该国针对番木瓜地方品种的遗传变异探索研究仍处于起步阶段。本研究旨在评估20份雌雄异株番木瓜基因型针对番木瓜白粉病（Streptopodium caricae）的抗性相关性状潜力。试验于温室中开展，采用随机区组设计（randomized block design），设置4次重复，每小区种植1株植株。本研究测定了带有白粉病症状的叶片发病率，以及第5、7叶位的白粉病病情严重度。所得数据经方差分析（analysis of variance）与最小二乘法均值比较检验处理；同时通过混合模型（mixed models）估算了白粉病发病率与病情严重度的方差组分及子代遗传值。结果表明，开展番木瓜白粉病抗性选择具备有利条件，其遗传力（heritability）介于51.57至67.82之间，选择准确度（selective accuracy）高于70%。其中PMI1、PMI6、PMI8、PMI11、PMI12与PMI15表现突出，具备降低叶片白粉病发病率与病情严重度的应用潜力。