Granular Pesta formulation of Fusarium oxysporum f. sp. orthoceras for biological control of sunflower broomrape: efficacy and shelf-life

Formulation of fungal propagules encapsulated in a wheat-gluten matrix (termed P̀esta') has proved to be a suitable technique for the development of Fusarium oxysporum f. sp. orthoceras (FOO) as a bioherbicide for sunflower broomrape (Orobanche cumana). To improve the efficacy of this fungus, 19 Pesta formulations, using two types of fungal spores and 8 adjuvants, used singly or in combinations, were examined for their shelf-life and for efficacy under greenhouse conditions. Amending Pesta with yeast extract reduced the loss of viability of microconidia and chlamydospores during production of the formulations by 40 and 100%, respectively. Sodium alginate and Water Lock also prevented loss of viability of chlamydospores during Pesta production. The longest shelf-life (inoculum viability) was obtained when granules were stored at 3 degrees C. In greenhouse experiments, there were no differences among the 19 Pesta treatments in disease severity (DS). In terms of the number of Orobanche attachments, Orobanche dry matter, and the number of Orobanche shoots that produced seeds, the most effective formulations were Pesta 14 (containing chlamydospores [PC] with yeast extract, glycerol, and sucrose as additives), Pesta 1 (containing microconidia [PM] with yeast extract and sucrose), Pesta 5 (PM with yeast extract, glycerol, and sucrose), Pesta 7 (PM with sodium alginate as an additive), and Pesta 15 (PC with stillage). These formulations produced 99, 98, 98, 97, and 97%, DS, respectively, and caused reduction in Orobanche biomass by 80, 76, 71, 80, and 67%, respectively. These Pesta formulations of FOO increased sunflower seed yield by 5-11 times in comparison with the negative control inoculated with fungus-free Pesta. In general, applications of the formulations of FOO in Pesta did not affect the number of leaves, stem diameter, plant height, or the dry matter of roots of sunflower or the rate of photosynthesis in sunflower plants.