Agronomic and Physiological Constraints to the Productivity of Tropical Grain Legumes and Prospects for Improvement

Abstract

Growth and development of the tropical grain legumes are generally highly sensitive to photothermal regime, so that seasonal and regional effects on phenology and yield potential can be large. Yet failure adequately to recognize and fully exploit the consequences of genotype X latitude/sowing date X density interactions has frequently constrained both agronomic and genetic advance with these species. Thus there is opportunity for short term productivity improvements through agronomic strategies which accept the implications of phenological plasticity, and seek to optimize management practices such as sowing date and sowing density, to exploit more effectively the yield potential and broaden the adaptation of existing cultivars. The greatest physiological potential for genetic improvement in the productivity of the tropical grain legumes lies not with increasing total biomass, but with increasing the proportion of biomass partitioned into seed, i.e. with improved harvest index (HI). There are difficulties in selecting for higher HI, including its association with phenology, although the latter provides the most powerful tool for manipulating HI in the short term. As with the cereals, more productive genotypes are likely to be characterized by reduced sensitivity to photothermal conditions, shorter growth duration, a more synchronous reproductive ontogeny, and greater HI, than is typical of traditional cultivars. Accordingly, optimal sowing densities will be higher, and crops will need more inputs, better management and more effective protection, than afforded to them in subsistence systems of production. Moreover, the increases in productivity will be achieved, at least partially, at the expense of the potential for yield homeostasis in adverse environments, and of non-seed components such as forage, fuel or tubers -attributes that are often highly valued in subsistence agriculture where many of the tropical food legumes are presently grown. Improvement programmes will therefore need to adopt strategies in particular situations which reflect local perceptions of the importance of productivity improvement relative to that of minimizing inputs and risk.R. J. Lawn: Limitaciones agronomicas y fisioldgicas en la productividad de granos leguminosos tropicales y perspective para el mejoramiento. RESUMENPor lo general, el crecimento y el desarrollo de los granos leguminosos tropicales son sumamente susceptibles al regimen fototermico, de modo que los efectos estacionales y regionales sobre la fenologia y el potencial de rendimiento son grandes. Sin embargo, el no reconocer bien y explotar al maximo las consecuencias de las interacciones genotipo X latitud/fecha de siembra X densidad ha limitado con frecuencia los avances agronomicos y geneticos en estas especies. Existe pues la oportunidad de mejoras en la productividad a corto plazo mediante estrategias agronomicas que acepten las implicaciones de la plasticidad fenologica y que busquen perfeccionar las practicas de gestion tales como la fecha y densidad de siembra, para...

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