From a practical point
of view the cultivars which produced well under a
low level of P and responded well to added P are the
most desirable. Cultivars such as CNA 5164, CNA
4097, CNA 5170, IR 3646-8-1-2, CNA 4137, A8-
391 and IAC 47 fall into this category. High shoot
growth of these varieties is also asssociated with
high root growth. This means that P uptake efficiency
may be related to root growth. Extensive
root growth under conditions of low P availability
in soils might be a genetic characteristic of considerable
importance in areas in which soils are low
in available P and in which economic constraints
limit rates of fertilizer application.