Anthracnose resistance induction in chilli by electron beam irradiation.

Abstract Chilli seeds were irradiated with 0.3 kGy at 8 MeV from the electron beam source at the Thailand Institute of Nuclear Technology. M1 seeds were planted in Sukhothai Horticultural Research Centre and from these the line CA1131 was selected as suitable for growing in this area. Thirty anthracnose-resistant M2 chilli plants were selected after the appearance of anthracnose disease, caused by Colletotrichum gloeosporioides, in Sukhothai province from an initial M1 mutant population of 123 individuals. However, chilli fruits from 17 plants showed resistance after laboratory inoculation experiments. These chilli plants were crossed with the 'Hoarue Huaisai', which has large fruit. The F2 progenies were selected for anthracnose resistance and large fruits. Two hybrids with anthracnose resistance (derived from the cross CA1131 × 'Hoarue Huaisai') were identified and used for field anthracnose resistance tests in 2015. Resistant plants with large fruits were discovered in the F3 inbred line no. 6-1-4 grown during the dry season, but this line did not show strong disease resistance in the rainy season. A further 63 F5 inbred lines showed anthracnose resistance in the field experiment. Five samples per line of each of the 63 inbred lines were inoculated in the laboratory at Thailand Institute of Nuclear Technology. The fruits of inbred line no. 32-2-8 showed complete anthracnose resistance and seven lines were segregating as resistant. All eight of these lines are being used in the ongoing chilli project aimed at developing chilli varieties with broad resistance to anthracnose caused by three Colletotrichum species that are prevalent in Thailand.