Isolation of sources of combined resistance to purple blotch, basal rot and white rot in onion (Allium cepa L.)

Abstract

Study was conducted to identify sources of multiple resistance to purple blotch, basal rot and white rot diseases in onion by screening 50 genotypes using seed, bulb and seedling inoculation methods both under natural and artificial epiphytotic conditions, and to evaluate biochemical and morphological factors responsible for disease resistance. The lines YL-58.WPL-95, 73, Pusa Red-135, Kalipathia Local-303, MS-48-26 and MS11-36 showed multiple resistances for purple blotch, basal rot and white rot diseases. Moderate resistance to purple blotch and white rot was notice in Sel 14-2, YL-61, WPL-95, MS65- 11, MS-65XPBR-415 and MS11XPBR-409. Screening at seed stage revealed that 19 genotypes were resistant (81-100%) to purple blotch,13 moderately resistant to (61-80%) basal rot and only one genotype YL-68 moderately susceptible(41-60%) to white rot. Screening at bulb stage the genotypes Sel 14-5, Sel 13-26, WPL-158, 165, 169, PWO-1- PAU-309, MS-48-25 were found to have moderate multiple resistance to basal rot and white rot. However, five genotypes each for basal rot and white rot were found resistant (Rose-69,WPL-95,169,PBR-5PAU-306 and AK-IIHR-307) and (WPL-69, PBR-5-PAU- 306, Pusa Red-135, MS(YL) Pure(s)-414, respectively). Screening at seedling stage in open field revealed that the lines Sel 11-34,MS65-8,9,and MS65XPBR-415 to had multiple resistance to purple blotch and basal rot, and lines WPL-158,169,73,AK-IIHR- 307 and MS48-100 were moderately resistant. Plant screening in polyhouse revealed that none of the onion genotypes were resistant to purple blotch, basal rot and white rot. However, moderate resistant was observed in seven genotypes (WPL-169, 158, 165, MS48-25, PWO-1-PAU-309, Sel13-26 and Sel 14-5). The biochemical studies indicated that the resistant varieties recorded high reducing sugars and phenols as compared to susceptible ones. Onion plants with tubular (erect) leaves were found to be moderately resistant to purple blotch.