A definition of the optimal allocation of effort in conservation of plant genetic resources-with application to sample size determination for field collection

Summary A criterion was presented to define the most efficient strategy for the exploration and maintenance of plant genetic resources. All of the three factors composing the efficiency. i.e., multiplicity of target populations. the amount of expenses, and goodness for individual populations of the conservation manipulation adopted, were incorporated in the present criterion. Sample size per target population for field collection was investigated on the basis of this criterion, leading to the conclusion that the number of visited populations rather than sample size per population determines the overall efficiency of a collection project as a whole. Without any particular reason, intensive sampling for a limited number of populations is not logical. A sample size as small as ten plants per site or population was estimated reasonable to cover a large target area.     

Genetics of genetic conservation. II. Sample size when collecting seed of cross-pollinating species and the information that can be obtained from the evaluation of material held in gene banks

Summary Provided that the seed collected from each plant in natural populations of a species is kept separate from that of every other, a rough estimate of the heritability of a quantitative character can be obtained from the natural progenies raised from this seed in a randomised evaluation trial; a knowledge of the reproductive biology of the species can help to make this estimate of the heritability of the character more precise.The theory employed in this evaluation procedure can be used to investigate the possibility of reducing the number of plants visited in a population, when species set all of their seed by cross-fertilisation, by taking several seeds from each. We show that it is not worth taking more than eight seeds from each plant and that, in the absence of precise information about the paternity of this seed, it might be better to follow the general recommendation of Lawrence et al. (1995), by taking only one seed from each of the 172 plants.Having investigated the minimum sample size for genetic conservation in the narrow sense, we broaden discussion to consider sample size for evaluation and regeneration. It is pointed out that it is not necessary to take more than about ten seeds from each of 20–30 randomly chosen plants in each population visited and that it is possible to reduce this number of plants if material from a number of populations is evaluated in a single trial. Finally, we draw attention to the possibility of regenerating seed from a composite population founded by raising one plant from the seed taken from each plant of the original collection, as an alternative to regenerating the seed of each accession independently from that of every other.     

Comparison of heritabilities derived from single F2 seed populations and bulk seed from F2 plant populations for oleic,linoleic and linolenic acids in oilseed rape

Summary The heritabilities for oleic, linoleic and linolenic acids in oilseed rape (Brassica napus) were determined using single F₂ seeds on F₁ plants and bulk seed samples of F₂ plants. The heritabilities by the use of single F₂ seeds were found to increase, remain constant, or decrease relative to those obtained from F₂ plant populations, depending on the fatty acid and the cross. However, the change in heritabilities was not great in most cases. Therefore the half-seed technique could be used for early generation selection for these fatty acids.     

Farmers' seed management practices open up new base populations for pearl millet breeding in a semi-arid zone of India

Farmers in western Rajasthan (north‐west India) produce and maintain their landrace populations of pearl millet through their own distinct seed management practices. The objective of this study was to characterize morphological and agronomic variability of different traits between and within three farmers' populations using quantitative‐genetic parameters. Populations examined were a typical landrace and two modified landraces, which were generated through farmer introgression of modern varieties with different levels of subsequent selection. From these three populations, 100 random full‐sib progenies were evaluated in field trials at two locations in western Rajasthan over two years. Significant genetic variation existed within the three populations. Estimates of heritability were moderate to high for all observed traits. Predicted selection response for grain yield across environments was 1.6% for the typical landrace and 2.2% for both the modified landraces. Results suggest that the introgression of modern varieties into landraces had increased the genetic diversity. Therefore, farmers' current breeding activities could open up new resources for plant breeding programmes aiming at plant improvement for the semiarid zones of India.