Induction of Defense-Related Enzymes and Pathogenesis-Related Proteins Imparts Resistance to Barley Genotypes Against Spot Blotch Disease

Spot blotch caused by Bipolaris sorokiniana is a major foliar disease of barley affecting its productivity worldwide. The barley cultivar with complete resistance to this pathogen is not yet identified. In the present study, leaves of six barley genotypes namely PL 807, BH 946, DWRUB 52, BL 1338, BL 1369 and PL 426 inoculated with Bipolaris sorokiniana were evaluated for levels of H2O2, malondialdehyde, antioxidative enzymes, non-enzymatic antioxidants, pathogenesis-related (PR) proteins and β-glucan. The disease score was assessed at flag leaf (F) and one leaf lower to the flag leaf (F1) at two growth stages, i.e. GS 55 and GS 87. The genotype BL 1369 showed moderately resistant nature, PL 807, DWRUB 52 and BL 1338 moderately susceptible whereas other genotypes remained susceptible in response to this pathogen. During GS 87 stage, maximum increase of catalase (CAT), ascorbate peroxidase (APX), glutathione reductase (GR), phenylalanine ammonia lyase (PAL), tyrosine ammonia lyase (TAL) and polyphenol oxidase (PPO) activities along with concomitant decrease of H2O2 content in the infected F1 leaves of BL 1369 may contribute towards its moderately resistant character. However, downregulation of APX and GR enzymes in PL 426, BH 946 and DWRUB 52 may be responsible for their sensitivity towards this pathogen. Although on fungal inoculation, chitinase activity increased in all the genotypes except DWRUB 52 and BL 1338 but maximum increase was reported in BL 1369. β-glucanase activity also increased significantly in both the leaf tissues of BL 1369. It showed positive correlation with chitinase in the flag leaf at 1% level of significance. The β-glucan content decreased in DWRUB 52 and PL 426 upon fungal infection while it increased in BL 1338 and BL 1369 which further pointed out towards resistant character of BL 1369 as the cell wall is a physical barrier which constitutes the first line defence against pathogen attack.