Assessing germplasm collections for traits useful in plant nutrition

Abstract

In the past, empirical selection by breeders has been successful at changing such regulatory processes as the pattern of partitioning and the timing of development. It has done little to increase the efficiency of the major metabolic or assimilatory processes, such as photosynthesis or nutrient use efficiency. A number of possible agents of change to develop crop varieties that produce greater yield per unit of nutrient are available. A combination of enhanced use of limited nutrients and better extraction of available nutrients from the soil would likely result in the best possible option for crops grown under low-nutrient conditions. The unpredictable nature of such conditions will require plasticity to efficiently use a sustainable portion of the available nutrients, irrespective of the source. The primary agent of change will be a source of genetic variation for the trait of interest. The two main options are intra-specific or inter-specific genetic variation. Intra-specific variation is more easily exploited by the plant breeder, but is less likely to exist, except in crops where the evolution has included significant production under very diverse marginal conditions. A more likely source of significant variation will be differences among species that have evolved under distinctly different environments, such as the wild relatives of the crop. The objective of this review is to explore the various agents of change required for enhanced nutrient use efficiency. A number of studies have been undertaken in sorghum to assess the value of intra-specific and inter-specific variation as improved sources of drought tolerance and nutrient use efficiency (NUE). A number of accessions were identified based upon an assessment of the various components of these two traits within very diverse germplasm. The key to progress in breeding nutrient use efficient cultivars will be in the enhanced utilization of genetic resources. Intra-specific strategies will concentrate on the use of landraces or farmer varieties and wild relatives in the primary genepool. The use of these sources could be direct, but could involve backcrossing to minimize the impact of undesirable alleles. The secondary and tertiary genepools might serve as very important sources of unique alleles. One option for the future will be the use of gene mapping and isolation. Once isolated and sequenced the gene can be directly introduced into the crop cultivars with transformation. This same approach could be used in unrelated species where mechanisms are carefully evaluated using comparative approaches.