Role of foliage component and host age on severity of Alternaria leaf spot (caused by Alternaria japonica and A. brassicae) in canola (Brassica napus) and mustard (B. juncea) and yield loss in canola

摘要: Studies were undertaken under controlled conditions into the effects of different foliage components (cotyledon, first, second and third leaf) at three plant ages (3, 5 7 weeks old) on development Alternaria leaf spot disease, caused by japonica or A. brassicae, in canola (Brassica napus cv. Thunder TT) mustard (B. juncea Dune). generally showed percentage disease index (%DI) values similar to brassicae across two Brassica species, ages. %DI from either pathogen was greater older plants than younger for same both cultivars. Field studies then with compare (leaf, pod stem) consequent adverse impact seed yield. more severe terms area diseased (%LAD 62.6) stem (%SAD 69.8) (%PAD 25.5), whereas leaves 61.9) pods 47.4) stems 41.0). Stem incidence (%SDI 94.0) 56.5), but (%PDI 93.5) 86.1). For japonica, AUDPC (LDI, 283.5), (LAD, 253.3) collapse (LCI, 149.5) resulted a yield loss 58.1%, where LDI (277.8), LAD (247.2) LCI (111.0) 59.4%. These findings explain observed acceleration severity as through growing season become susceptible increasing age, susceptible, later developing abundant. first time, we demonstrate that conducive field development, can cause serious seed-yield losses magnitude those occurring brassicae.