Efficacy of seed defense proteins in biofortified pearl millet lines against blast and downy mildew

Abstract

Pearl millet is a nutritious and climate-resilient dryland cereal crop. The present study was conducted to identify the defense proteins in seed extrudes of 25 biofortified (Fe and Zn) inbred lines, and investigate their efficacy against blast (isolates Pg 45, Pg 138, and Pg 186) and downy mildew (isolates Sg 409, Sg 445, and Sg 576) diseases. The study revealed the presence of cysteine protease inhibitors (4.3–58.5 units/mg) as well as pathogenesis-related (PR) hydrolases including chitinases (5.3–16.3 units/ml), β-1,3-glucanases (7.3–32.9 units/mg), and cellulases (0.19–4.11 units/mg) in the test lines. The activity levels of cystatins and PR hydrolases in the pearl millet lines were in relative consistency with the resistance levels observed in the greenhouse screenings against blast and downy mildew diseases. Furthermore, antifungal screenings of seed proteins against blast pathogen exhibited a significant reduction in radial growth of Pg 138 (57%) followed by Pg 186 (13%) and Pg 45 (10%). Spectrophotometric assays (A595) exhibited significant retardation in spore germination and initial growth (48 h) of Pg 45 (53.8–87.3%) followed by Pg 186 (19.2–61.3%) and Pg 138 (1.5–36.7%). Furthermore, seed proteins of biofortified lines efficiently reduced the downy mildew disease incidence in greenhouse screenings by seed treatments of susceptible pearl millet lines ICMP 451 (0.6–36% against Sg 409; 32–61% against Sg 576) and 7042R (14–80% against Sg 445). The results of this study will provide insight into the biochemical basis of resistance in pearl millet against foliar blast and downy mildew diseases, and to exploit novel strategies for breeding for disease resistance.