Biocontrol Activity of Yeasts against Alternaria solani and Plant Growth Promotion of Tomato Plants

Aim: Yeasts have emerged as a single celled biocontrol agent which are applicable in controlling many disease causing pathogens in plants. These yeasts also have growth promoting substances that help in the growth and development of plants.

Materials and Methods: Yeast on tomato plants were isolated using standard plate count technique and observed under microscope for their cell shape and sizes. Biocontrol activity of yeast was evaluated by measuring diameter of zone of inhibition (mm) and estimating mycelial dry weights of pathogen. IAA production by yeasts was estimated in vitro and the plant growth and development was evaluated by measuring plant heights, number of leaves, number of days for flower initiation, shoot biomass, root mass, disease incidence and severity in pot culture experiments.

Results: Yeast isolate TPL-I isolated from tomato plants was most effective in inhibiting Alternaria solani with diameter of zone of inhibition of 9.00 mm. Reduced mycelial dry weight of pathogen viz., 40.07 mg was exhibited by TPL-I under in vitro conditions. The maximum concentration of IAA was produced by TPL- I (0.11 μg/ml). The highest plant height, number of leaflets and number of days taken for flower initiation was recorded highest in T4 (Trichoderma harzianum) followed by T7 (Foliar spray of Alternaria solani + TPL- I + Trichoderma harzianum) at 30, 45 and 60 days after transplanting. Maximum dry weight of shoot (12.32 g/plant) and root (5.18 g/plant) was recorded in T4 (Foliar spray of Trichoderma harzianum) whereas, minimum dry weight of shoot (8.26 g/plant) and root (2.80 g/plant) was recorded in T2 (Foliar spray of Alternaria solani). Lowest disease incidence (33.33%) and disease severity (24.25%) was recorded in T5 (Foliar spray of Alternaria solani + TPL- I).