A unified presentation, a synthesis, and an evaluation of the methods employed in the estimation of heritability in plants are presented. Asexual, cross‐fertilizing, and self‐fertilizing diploid species, as well as annual and perennial ones, are considered. All broad‐ and narrow‐sense heritabilities are defined on individual and family bases for prediction of response to selection for a target population of environments in space and time. Narrow‐sense heritabilities are defined in cross‐fertilizing species for expected response to variations of mass, half‐sib, and full‐sib family selection for the next generation and the long term, and similarly in self‐fertilizing species. The use of both collateral and lineal relatives to estimate heritability is discussed, and the biases present in the estimators are given. Many departures and variations of the common procedures are discussed. The standard errors of heritability estimators and confidence intervals are presented.

Estimation of heritability and prediction of selection response in plant populations

Haploids are plants with a gametophytic chromosome number and doubled haploids are haploids that have undergone chromosome duplication. The production of haploids and doubled haploids (DHs) through gametic embryogenesis allows a single-step development of complete homozygous lines from heterozygous parents, shortening the time required to produce homozygous plants in comparison with the conventional breeding methods that employ several generations of selfing. The production of haploids and DHs provides a particularly attractive biotechnological tool, and the development of haploidy technology and protocols to produce homozygous plants has had a significant impact on agricultural systems. Nowadays, these biotechnologies represent an integral part of the breeding programmes of many agronomically important crops. There are several available methods to obtain haploids and DHs, of which in vitro anther or isolated microspore culture are the most effective and widely used. This review article deals with the current status of knowledge on the production of haploids and DHs through pollen embryogenesis and, in particular, anther culture.

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Anther culture for haploid and doubled haploid production

In earlier works, the author reviewed and emphasized the importance of the in vitro induction of haploids (Reinert and Bajaj 1977; Bajaj 1983 a). During the last decade tremendous progress has been made in this area. The frequency of androgenesis has been increased, work extended successfully to a number of agricultural crops, and new cultivars have been released. This warrants the need to put this information and literature together.

In Vitro Production of Haploids and Their Use in Cell Genetics and Plant Breeding

The microspore is at the centre of a variety of topics in modern plant science and breeding Isolated microspore cultures have the remarkable quality of resembling the alternation of generations in the life cycle of angiosperms, ie the change between the diploid sporophytec and the haploid gametophytec generation Although the natural destination of microspore development is to differentiate into mature pollen and accomplish fertilization, isolated and in vitro cultured microspores or young pollen grains can either differentiate into mature, fertile pollen (the male gametophytes) by culture in a rich medium without stress, or divide repeatedly and develop into embryos (sporophytes) after a stress treatment As experimental systems, microspore cultures are used to investigate pollen development and pollination, embryogenesis, totipotency, cytodifferentiation, cell cycle, phase change and the role of stress in development As a tool in genetic engineering, they can be used to produce doubled haploids (recombinant inbreds) for plant breeding and gene mapping, to overcome crossing barriers (male sterility and self-incompatibility), to induce and select for mutants and to create transgenic plants In this review genetic, cell biological and molecular aspects of in vitro microspore development are presented and put in the context of current basic and applied plant science

The microspore: A haploid multipurpose cell

The in vitro development of a whole plant from a single cell (eg microspore or somatic cells) is a characteristic feature of plants. The amenability of a plant to in vitro culture is influenced by the genotype, which is thus of major importance in the plant tissue culture response. The differences observed between different cultivars during in vitro tissue culture with respect to embryogenesis and regeneration result from quantitative or qualitative genetic differences. We describe results obtained from quantitative genetic studies, from Mendelian genetic analysis and from gene mapping. It is less easy to study the influence of cytoplasmic genomes. Moreover, it is necessary to discriminate between maternal effects and cytoplasmic inheritance. A conclusion from this review is that the choice of parental strains for a breeding program should be realized on agronomic criteria rather than on compatibility with the tissue culture technique used. Fortunately, it is relatively easy to incorporate short-term tissue culture capacity into agronomically valuable genotypes. This is of major interest since tissue culture remains necessary for most aspects of crop plants biotechnology. Very little is known about the molecular events that trigger in vitro embryogenesis and regeneration. It is clear that genes involved in the tissue culture response are not specialised ‘tissue culture genes’.

Genetic analysis of in vitro plant tissue culture responses and regeneration capacities

Anther-culture response was examined among three spring wheat (Triticum aestivum L.) cultivars to evaluate the genetic component of response and to determine whether androgenetic performance could be improved by selection. The three lines, the three possible F1's among the three lines, their F2's, and the backcrosses to the parents were evaluated for callus production and regeneration capacity. Significant variation was observed among the generations of the three crosses for callus formation. Genetic variation for regenerability was nonsignificant. Callus production was negatively correlated (-0.24) with regeneration capacity. The random variation in the study was too great to determine whether major-gene differences for antherculture response exist among the three lines by examining population distributions. When the material was evaluated for quantitative gene effects, the estimates for the additive gene effects were generally greater than the estimates for the dominance gene effects for callus formation. Only the Pavon x Chris cross, however, exhibited a significant narrow sense heritability estimate for callusing response (0.94). Due to the large component of random variation and the varying selection potential among crosses for androgenetic performance, improving anther-culture response in wheat by selection could prove difficult unless the anther-culture process itself selects for response traits at the gametic level.

Genetic analysis of the anther-culture response of three spring wheat crosses.

Two regeneration systems for the production of haploid plants from wheat anther culture

Anther-derived, doubled haploid populations were obtained from two hard red winter wheats, 'Centurk' and NB88. Spontaneous doubling frequency, efficiency of colchicine treatment, and vernalization ...

S. G. Metz

Papers

Genetic analysis of the anther-culture response of three spring wheat crosses.

Two regeneration systems for the production of haploid plants from wheat anther culture

Chromosome doubling and aneuploidy in anther-derived plants from two winter wheat lines