Corm Rot and Yellows of Gladiolus and Its Biomanagement

Abstract

A corm dressing containing Trichoderma harzianum (T014) and Pseudomonas fluorescens (PS07) cultured on a bagasse-soil-molasses mixture was tested for its efficacy against corm rot and yellows caused by Fusarium oxysporum f. sp. gladioli on the gladiolus (Gladiolus psittacinus L.) cv. White Prosperity (WP), King Lear (KL), Friendship (FR), Her Majesty (HM) and American Beauty (AB) in a pot culture experiment. The effectiveness of the biocontrol agents was compared with that of the fungicide carbendazim (200 ppm). All cultivars were susceptible to the pathogenic fungus and developed the characteristic symptoms of corm rot and yellows. Cultivars HM and AB were highly susceptible, scoring 2.9–3.2 on a corm rot and yellows scale (0–5 scale; compared with 1.5–2.9 for the other cultivars). Fungal infection reduced plant growth and flowering significantly, with a 15–28% decrease in the number of florets/spike. Application of carbendazim, T. harzianum (P=0.001) and P. fluorescens (P=0.05) decreased the corm rot and yellows scores and the soil population of the pathogen, and increased plant growth and flowering. The greatest improvement in the flower variables of infected plants was recorded with P. fluorescens (+18–31% over control). The soil population of the bioagents increased significantly over time, both in the presence and in the absence of the pathogenic fungus, but more in its absence.