Roots are Targets of Multiple Stresses in Various Tropical Crops

Marco V. Gutiérrez (University of Costa Rica, Fabio Baudrit Exptl. Stn., Alajuela, Costa Rica)

Yields of tropical cash and subsistence crops are substantially lower than those achieved outside their tropical centers of origin and cultivation; differences between record and mean yields obtained in farms are abysmal. Several abiotic and biotic stresses and their combinations, many originated in the soil (drought, flooding, root-rots) are cited as causes of these yield losses. However, the role of roots as interface between the soil environment and the symptomatic shoot has been overlooked. For instance, poor sampling and classification protocols are often used, and seasonality is ignored when monitoring root dynamics and functionality. We approached various widespread physio-pathological disorders in the field using an integrative approach, measuring plant responses (gas exchange, water and nutrient profiles) along the soil-plant-atmosphere continuum and during whole climatic cycles (rainy and dry seasons). We examined the roots of pineapple, oil palm, banana, coffee, common bean, and tree crops using different techniques: excavations, systematic sampling, quantitative image analyses and rhyzotrons. Observations were carried-out in farm, greenhouse, and forest settings. In all cases, poor root quality and quantity and root decline preceded the occurrence of above-ground syndromes. Root decline was involved in the chronical incidence of oil palm spear-rot. Low root quantity and quality were associated to the lodging and uprooting of bean, banana and forest trees; and root water status was crucial in the control of flowering in coffee and citrus orchards. In pineapple, all root types absorbed nutrients actively, while deficient roots and root hairs were associated with natural flowering, movement of microbes to the shoots and physio-pathological syndromes in crowns and fruits. Root systems are the interphase of complex soil-shoot relations that must be considered in all interventions to improve soil health and the agronomic performance of tropical crops.