Suitability of certain strawberry genotypes for breeding of new cultivars tolerant to leaf diseases based on their combining ability

The aim of the study was to estimate the general and specific combining abilities (GCA and SCA) of 13 dessert strawberry cultivars: ‘Figaro’, ‘Salsa’, ‘Palomar’, ‘Granda’, ‘Camarosa’, ‘Elianny’, ‘Aromas’, ‘Diamante’, ‘Portola’, ‘Charlotte’, ‘San Andreas’, ‘Monterey’ and ‘Albion’ for tolerance to the major leaf diseases strawberry leaf spot (Mycosphaerella fragariae (Tul.) Lindau), leaf scorch (Diplocarpon earliana (Ell. & Ev.) Wolf) and powdery mildew (Sphaerotheca macularis (Wallr.) U. Braun). The crossing programme was performed in the winter of 2010/2011 in the glasshouse following a half-diallel cross mating design (Griffing’s method IV). Progenies of the 78 newly obtained families were evaluated in field conditions (randomized complete block design, 4 replicates, 15 plants per plot). Observations of the severity of plant infection with leaf spot, leaf scorch and powdery mildew were recorded from 2011 to 2013. Statistical analysis of data was performed according to Griffing’s fixed model. The most numerous significant and positive GCA effects were estimated for cv.‘Salsa’ for low plant susceptibility (tolerance) to all three diseases assessed. High GCA effects were also showed for cvs ‘Figaro’ and ‘San Andreas’—for low plant susceptibility to leaf spot and leaf scorch, and for cv.‘Diamante’—for low plant susceptibility to leaf spot and powdery mildew. Lower breeding values for the estimated traits were observed with cv.‘Camarosa’—for low susceptibility to leaf spot; with cvs ‘Palomar’ and ‘Granda’—for low plant susceptibility to leaf scorch, and with cvs ‘Monterey’, ‘Portola’ and ‘Charlotte’—for low plant susceptibility to powdery mildew. The lowest GCA effects for low plant susceptibility to the all three leaf diseases tested were observed with cv.‘Albion’. High usefulness for breeding new, resistant varieties has also been observed in the combination ‘Aromas’ × ‘Elianny’, which has significantly negative SCA effects for the susceptibility of plants to both strawberry leaf spot and leaf scorch.