Induction of Systemic Resistance of Cucumber to<i>Colletotrichum orbiculare</i>by Select Strains of Plant Growth-Promoting Rhizobacteria

TLDR

The study screened 94 PGPR strains on cucumber, identified six that induced systemic resistance, and confirmed root colonization by rifampicin‑resistant mutants at densities of 10^6.5–10^8.3 cfu g⁻¹ at 7 days and 10^4.1–10^6.1 cfu g⁻¹ at 21 days. Treatment of cucumber seeds with these six PGPR strains significantly reduced lesion size, produced HCN in four strains, and led to less root necrosis, supporting that seed‑applied PGPR can induce systemic resistance to C.

Abstract

Ninety-four strains of plant growth-promoting rhizobacteria (PGPR) were screened for induction of systemic resistance using a model system of cucumber and anthracnose, caused by Colletotrichum orbiculare. Compared with a nonbacterized, challenged control, treatment of cucumber seeds with six PGPR strains resulted in a significant reduction in lesion size after challenge-inoculation with C. orbiculare. Four of the six PGPR strains that induced resistance in cucumber produced HCN in vitro. Antagonism in vitro toward Pythium ultimum, Rhizoctonia solani, and C. orbiculare on three media generally was absent with five PGPR strains and weak with one strain. Rifampicin-resistant mutants of the PGPR strains colonized roots at mean population densities of log 6.5 to 8.3 cfu g(-1) of root at 7 days after planting and log 4.1 to 6.1 cfu g(-1) at 21 days after planting. None of the strains was recovered from surface-disinfested petioles on the day of challenge with C. orbiculare. Roots from plants bacterized with PGPR strains showed less necrosis than the nonbacterized, challenged control. The results support the conclusion that some PGPR strains applied to seed can induce systemic resistance to C. orbiculare