Anaerobic soil disinfestation using locally available carbon sources as a potential management strategy for bacterial wilt in tomatoes

Abstract

Tomato production in Tanzania is far lower than the 27.5 t/ha global average. Important factors such as deteriorating soil fertility, using vulnerable and low-yielding varieties, unreliable rainfall, diseases, pests, and poor farming practices contribute to reduced tomato production. Bacterial wilt is the most devastating tomato disease in terms of yield losses and complicated management considering pathogen diversity and the soil-borne nature of the disease. On-farm trials and bioassays were conducted to determine the efficacy of anaerobic soil disinfestation (ASD) with wheat bran, rice bran, molasses, and cow manure as carbon sources in suppressing bacterial wilt disease of tomato. We established randomized complete block design (RCBD) experiments in nine fields in Misufini, Mlali villages in Morogoro and Image of Iringa region in mainland Tanzania. The bioassay experiment was also laid in a RCBD and conducted at Sokoine University of Agriculture (SUA) greenhouses using soil naturally infested with Ralstonia pseudosolanacearum collected from the same nine fields. The treatments reduced bacterial wilt incidence in tomatoes grown in ASD-treated soils compared to non-treated control soils in field trials at Misufini 1 (P=0.0205), Misufini 2 (0.0061), and Mlali 2 (P =0.019). There were no significant differences among ASD treatments with different carbon sources in disease incidence. This trend was also observed in the bioassays in which bacterial wilt incidence and area under disease progress curves in tomato seedlings grown in field-treated soils from Image, Mlali, and Misufini were significantly lower than in non-treated controls (P <0.0001). This study confirms that ASD can be used as an important suppressor of pathogens through a soil rejuvenation process that involves the creation of an anaerobic environment in water-saturated soil amended with high carbon-based organic materials.