Quantitative trait loci mapping of partial resistance to Diamondback moth in cabbage (Brassica oleracea L).

KEY MESSAGE: The resistance to Diamondback moth insect in cabbage is governed by many minor loci in quantitative nature, and at least four genetic loci should be incorporated in marker-assisted breeding program for developing partially resistant DBM cabbage cultivars. The Diamondback moth (DBM), Plutella xylostella (L.), is the most destructive insect infesting cruciferous plants worldwide. Earlier studies have reported that the glossy leaves of cabbage are associated with resistance to this insect. However, until now, genetics of DBM resistance has not been studied in detail, and no QTL/gene mapping for this trait has been reported. In this paper, we report quantitative trait loci (QTL) mapping of DBM-resistant trait using 188 randomly selected segregating F 3 population derived from crossing a partially DBM-resistant glossy leaf cabbage (748) with a susceptible smooth cabbage line (747). Quantitative trait loci mapping using phenotypic data of four consecutive years (2008, 2009, 2010, and 2011) on DBM insect infestation detected a total of eight QTL on five linkage groups suggesting that DBM resistance is a quantitative in nature. Of these QTL, four QTL, i.e., qDbm 1 on LG1, qDbm5 and qDbm6 on LG7, and qDbm8 on LG9, were detected in different tests and years. The QTL, qDbm6 on LG7, was consecutively detected over 3 years. Tightly linked molecular markers have been developed for qDbm8 QTL on LG9 which could be used in marker-assisted breeding program. Our research demonstrated that for desired DBM resistance cultivar breeding, those four genetic loci have to be taken into consideration. Furthermore, the comparative study revealed that DBM resistance QTL is conserved between close relative model plant Arabidopsis thaliana and Brassica oleracea genome.

Metabolic differentiation of diamondback moth ( Plutella xylostella (L.)) resistance in cabbage ( Brassica oleracea L. ssp. capitata).

The diamondback moth, Plutella xylostella (L.), is a major pest responsible for destroying cabbage and other Brassica vegetable crops. A diamondback moth-resistant cabbage line was studied by comparing its metabolite profiles with those of a susceptible cabbage. Fourier transform infrared spectroscopy analysis revealed that carbohydrates, aromatic compounds, and amides were the major factors that distinguished the resistant and susceptible genotypes. Gas chromatography-time-of-flight mass spectrometry profiled 46 metabolites, including 19 amino acids, 15 organic acids, 8 sugars, 3 sugar alcohols, and 1 amine in two genotypes and F1 hybrid cabbages. The levels of glycolic acid, quinic acid, inositol, fumaric acid, glyceric acid, trehalose, shikimic acid, and aspartic acid were found to be very significantly different between the resistant and susceptible genotypes with a P value of <0.0001. These results will provide a foundation for further studies on diamondback moth resistance in cabbage breeding and for the development of other herbivore-resistant crops.