Genetic variance and breeding values for resistance to a wind-borne disease [Sphaerotheca macularis (Wallr. ex Fr.)] in strawberry (Fragaria × ananassa Duch.) estimated by exploring mixed and spatial models and pedigree information

Abstract

A mixed model approach was used to estimate variance components and heritabilities for resistance to powdery mildew, a wind-borne disease in strawberry. In order to improve precision in the statistical computations, spatial error control effects were included to account for systematic environmental variations in the large field trials. Pedigree information was included where feasible. Seedling families obtained from an incomplete 63-by-63 diallel cross were grown at six locations and scored subjectively for mildew attack three times during the growing season. The 63 parents included both European and American cultivars as well as advanced selections from various breeding programmes. A total of 298 full-sib families were realized, including 26 reciprocal families. No reciprocal differences were found. On a plot-mean basis, the broad-sense heritability was found to be intermediate, H(2) = 0.44-0.50, depending on whether the pedigree information was included in the model or not. The increase was mainly due to a substantial increase in the additive variance component. Likewise, the narrow-sense heritability increased from h(2) = 0.39 to h(2) = 0.45 when the pedigree information was included, while the ratio of the specific combining ability variance to the general combining ability variance fell from 13% to 10%. The predicted breeding values of the 63 parents demonstrate that important cultivars such as Elsanta and Korona are unlikely to produce progenies with a high degree of resistance. On the other hand, the Norwegian cultivar Solprins, the Canadian cultivar Kent and the Italian cultivar Patty appeared to give highly resistant progeny. At the full-sib level, the estimated disease scores ranged from 1.15 (Kent x Induka) to 4.19 (Cavendish x Avanta), revealing a huge range of variation for powdery mildew resistance available for selection.

Identification of powdery mildew resistance QTL in strawberry (Fragaria × ananassa)

“…We found multiple QTL of small to moderate effect control disease resistance in both populations. Likewise, previous studies have found multiple small effect QTL which contribute to powdery mildew resistance in strawberry indicating quantitative resistance with both additive and non-additive genetic components (Simpson 1987; Nelson et al 1995; Davik and Honne 2005). …”

“…It was hypothesised that this may be attributed to low genetic variability in strawberry germplasm or low variation between mildew isolates (Xu et al 2008b). However, there is some evidence to suggest heterogeneity between populations of P. aphanis , namely the evolution of fungicide resistance (Sombardier et al 2010) and the resistance breaking in the cultivar Korona, likely due to the evolution of more virulent strains (Davik and Honne 2005). Reports of the production of ascospores in UK infections indicate the presence of a sexual cycle within powdery mildew (Xu et al 2008a), and high recombination associated with this life cycle typically leads to greater genetic diversity than observed in asexual reproduction (Barrett et al 2008).…”

BLUP for phenotypic selection in plant breeding and variety testing

“…Purba et al (2001) applied Bernardo's approach to predict performance of oilpalm (Elaeis guineensis) hybrids. Davik and Honne (2005) modeled GCA effects in a diallel experiment with strawberry (Fragaria spp.) using the A matrix ''under the usual assumptions of a large random mating parental population'', while SCA effects were assumed to be uncorrelated.…”

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

“…By contrast, Simpson (1987), while evaluating the progeny of remontant varieties of strawberry had proven that additive effects are dominant in the inheritance of the trait of powdery mildew susceptibility. Likewise, Davik and Honne (2005), MacLachlan (1978), and McNicol and Gooding (1979) had proposed a quantitative model of the inheritance of resistance to powdery mildew, in which the additive variance (GCA) is of a far greater importance, while the non-additive (SCA) effects, although also significant, are less important. In a study by Davik and Honne (2005), specific combining ability variance represented only 10-13 % of the total combining ability.…”