SCREENING PEANUT CULTIVARS IN THE FIELD FOR ROOT-GROWTH - A TEST BY HERBICIDE INJECTION IN THE SOIL

Breeding for deeper rooting may facilitate the development of improved cultivars in specific water-limited environments where water is available deep in the soil. Effective techniques for screening peanut (Arachis hypogaea L.) cultivars for differences in root growth under field conditions are not available as is the case for many other crops. A technique for such screening was evaluated. It consisted of injecting a herbicide (metribuzin=[4-amino-6-(1,1-dimethylethyl)-3-(methylthio)-1,2,4-triazin-5 (4H)-one]) in a 15-cm wide band into the soil, at a depth of 70 cm and at a distance of 45 cm from the rows of plants, which were parallel to the band, at a rate of 10 kg a.i. ha-1 of band. The soil was deep and sandy and the plants' water supply came from soil water reserves. The differences among the cultivars in the time of appearance of herbicide symptoms, and presumably their root extension rates, were highly significant for the seven cultivars tested. The advantages offered by metribuzin - rapid and uniform effect, clearly visible leaf symptoms and limited residual effect - are discussed, as is also the disadvantage of its destruction of test plants.