PHYSIOLOGICAL AND MORPHOLOGICAL ADAPTATIONS IN TOMATO INTERCROPPED WITH TAGETES ERECTA AND AMARANTHUS HYPOCHONDRIACUS

Abstract

Intercropping is an alternative strategy to traditional application of agrochemicals for plant disease management. Intercropping tomato plants (Lycopersicon esculentum Mill.) with marigold (Tagetes erecta L.) resulted in significantly less foliar and fruit damage by Alternaria solani. Such reductions were explained by the allelopathic effect of marigold on A. solani conidia germination, by the reduction in daytime hours with relative humidity ≥ 92 %, and by providing a physical barrier against conidia spreading. Physiological adaptations and anatomical modifications of tomato plants due to shading by marigold might also have some effect on A. solani infection. Therefore, in this study we measured net photosynthesis rate, respiration rate, stomatal conductance, chlorophyll content, leaf thickness, plant height, leaf area, specific leaf area and fruit yield of tomato plants intercropped with marigold or the native pigweed (Amaranthus hypochondriacus L.), or grown as a single crop. Tomato plants intercropped with marigold (T-M) or pigweed (T-P) grew longer stems (26 to 33 %), thinner leaves (33 to 35 %), and lower specific leaflet area (61 to 69 %) than plants grown alone (T). Also, tomato plants intercropped with marigold had a higher (P ≤ 0.05) net photosynthetic rate (48 and 64 %) and chlorophyll content (4 and 9 %) than T-P and T treatments, at 10 weeks after tomato transplant (WATT). From 19:00 to 23:00 h the T-M doubled (P ≤ 0.05) the respiration rate compared to the nonintercropped tomato plants. The amount of leaf sections with starch grains in the parenchyma cells was higher (P ≤ 0.05) in T-P (50 %) and T (86 %) treatments than in treatment T-M. Compared to treatments T-P and T, T-M produced more (P ≤ 0.05) fruits (100 and 148 %, at 8 WATT ), inflorescences (46 and 25 %, at 6 WATT) and fruit yield (100 and 148 % at 15 WATT ).