Combined Effects of Biosolarization and Brassica Amendments on Survival of Biocontrol Agents and Inhibition of Fusarium oxysporum

Abstract

Biocontrol agents (BCAs) added in the soil or applied to the seeds face many abiotic and biotic stress challenges. Only those BCAs that survive under harsh conditions perform well. Improving the survival of BCAs along with inhibiting the biotic stresses imposed by bacterial, fungal, and viral infections has been a major challenge in agriculture, especially in hot-arid climates. The present study aimed to evaluate the individual and combined effects of soil solarization and Brassica amendments on the survival of two biocontrol agents (BCAs), namely Trichoderma harzianum and Aspergillus versicolor, and on the reduction in a cumin wilt pathogen Fusarium oxysporum f. sp. cumini (Foc) in a field experiment conducted for two years under hot-arid climates. BCAs performed well in the solarized pots; it caused the maximum reduction in viable F. oxysporum propagules, significantly higher at 5 cm than at 15 cm of depth. Brassica amendment with BCAs caused a greater decrease in F. oxysporum propagules (95.7 to 96.7%) compared to a combination of BCAs and solarization (91.0 to 95.7%). Combining T. harzianum with A. versicolor increased the survival of T. harzianum, whereas integration with Brassica amendment could only improve the survival of T. harzianum at a depth of 5 cm and not at lower depths. The slightest decrease in A. versicolor population at high soil temperature was estimated when combined with T. harzianum. However, combining A. versicolor with Brassica amendment improved the survival of A. versicolor at high compared to low soil temperatures. Still, elevated soil temperature reduced the viable propagules. These studies demonstrate that both the native BCAs are compatible, and their integration with the Brassica amendment improves their survival and ability to reduce the population of cumin wilt pathogen. Thus, these BCAs with Brassica amendments can survive and perform well under hot-arid climates.