Postharvest Quality Characteristics and Sensory Evaluation of Intra and Interspecific Grafted Tomato (Solanum lycopersicum) Fruits

Abstract

Tomato (Solanum lycopersicum L.) is the second most important exotic vegetable widely consumed in Kenya. Its production constitutes one of the fastest growing markets in Kenya, edging towards a vital cash crop. Despite this, tomato production in the country has been declining in the past decade. This decline is attributed to a number of constraints in the value chain, including bacterial wilt disease complex caused by Ralstonia solanacearum that can devastate production, causing yield losses of up to 100%. More studies on solving tomato diseases by grafting tend to focus on production quantity but overlook the quality aspect of these grafted tomatoes. Numerous studies have reported the positive impact of grafting on tomato yields. However, grafting on different rootstocks has reported varying results on tomato quality. A clear understanding of the effect of grafting on tomato fruit quality can provide a guide in adopting grafting as an effective farming practice to solve the bacterial wilt problem in tomatoes, thus maximizing profits with minimal resource input that directly contributes to food and nutritional security. This study aimed to evaluate the postharvest quality and the sensory characteristics of intra- and interspecific grafted tomato fruit. Anna F1 and Cal-J, Kenyan commercial tomato varieties were interspecifically grafted on three African eggplant rootstocks; Manyire, AB2, and Sangawiri from World Veg. Centre, Arusha. The two varieties were also intraspecifically grafted on two wilt resistant hybrid tomato rootstocks; B.B and Armada from Takii Seed Company, Japan. The tomatoes were grown in a greenhouse and harvested at the mature green, turning, and ripe stages. The tomatoes were analyzed for size, weight, cumulative weight loss, texture, color changes, lycopene content, vitamin C, total soluble solids, total titratable acidity, respiration and ethylene gas production rates, and sensory evaluation. Interspecific grafting on Manyire green, AB2, and intraspecific grafting on Armada and B.B rootstocks significantly improved the physical and physiological attributes of the tomato fruit. There was a significant difference (p < 0.05) in the fruit size and weight of grafted tomatoes and control at all the three maturity stages. Intraspecific grafted tomato fruits on Armada rootstocks had the best quality characteristics in terms of firmness, low cumulative weight loss, respiration, and ethylene production rates associated with extended postharvest shelf-life. Intraspecific grafting reduced respiration and ethylene gas production rates with tomatoes from Anna F1 grafted onto Armada rootstocks attaining the least climacteric peaks of 20.20 ml CO2 Kg-1h-1 and 0.34 μL C2H4 Kg-1h-1 at the mature green stage, thus extending the postharvest life of these tomatoes. On the other hand, fruits from Cal-J grafted on Sangawiri rootstock had the highest ethylene production rate at 6.7 µl/kg/h in the ripe stage. Anna F1 tomatoes grafted onto B.B rootstock had the highest vitamin C content (28.11 mg/100g). Fruits from Cal-J grafted on Sangawiri reported the least sensory attributes in terms all the attributes assessed. Fruits from Anna F1 grafted on Armada reported the highest score in all sensory attributes evaluated; firmness (9.2), sweetness (9.1), juiciness (6.6), saltiness (9.3), overall look (9.4), and overall acceptability (9.3). On the other hand, the sensory attributes of tomato grafted on Sangawiri; are firmness (5.7), sweetness (5.1), saltiness (6.2), juiciness (6.4), overall look (5.5), and overall acceptability (5.3) had no significant difference (p< 0.05) from the nongrafted control. From this study, it is evident that the effect of grafting on tomato quality is dependent on hormonal and biochemical scion/rootstock interactions and a combination of both. Intra- and interspecific grafting on Manyire and AB2 rootstocks improved the physical, physiological, and sensory attributes compared to nongrafted control. However, biochemical quality was not affected upon grafting except Vitamin C and total soluble solids which were significantly improved and reduced respectively through intraspecific grafting. In general, grafted Anna F1 variety reported better quality traits than the Cal-J variety but were not significantly different. Intraspecific grafting had the best quality traits over interspecific grafting, with Armada rootstock reporting the best tomato quality. However, interspecific grafting on Manyire and AB2 rootstocks had comparable fruit quality to intraspecific grafting. Therefore, they could be adopted to complement the existing wilt management chemical methods.