In order to obtain an overview of the genetic diversity present within the set of pea cultivars released in Germany, 21 cultivars were analysed at the DNA level by random amplified polymorphic DNAs (RAPDs) and amplified fragment length polymorphisms (AFLPs), as well as for agronomic traits. Yield of grain cultivars ranged from 2.95 to 3.87 t/ha. Based on the screening of 60 RAPD primers and 32 Eco RI + 3/Mse I+3 AFLP primer combinations, 20 RAPD primers and 11 Eco RI + 3/MseI+ 3 primer combinations generating polymorphic and distinct fragments were chosen for estimation of genetic diversity. Twenty RAPD primers amplified a total of 314 scorable bands ranging from about 262 bp to 1996 bp. Of these, 175 fragments (55.7%) were polymorphic. Based on these data, genetic similarity (GS) was estimated between 0.80 (‘Lisa’ vs.‘Grapis’) and 0.94 (‘Bohatyr’ vs. ‘Sponsor’; mean GS = 0.88). Eleven AFLP primer combinations led to the amplification of 949 scorable fragments ranging from 43 to 805 bp and of these, 462 (48.7%) were polymorphic. Genetic similarity based on AFLPs was calculated between 0.85 (‘Lisa’ vs.‘Laser’) and 0.94 (‘Bohatyr’ vs. ‘Sponsor’, mean GS = 0.90). Correlation of genetic similarity estimated on RAPDs and AFLPs was estimated at r = 0.79** using Spearman's rank correlation coefficient and at r = 0.84 by the Mantel test, respectively. UPGMA cluster analysis carried out on these data separately for RAPDs and AFLPs and on the combined data reflected, to some extent, pedigree relationships and cophenetic correlations (r = 0.89 for RAPDs, r = 0.88 for AFLPs, and r = 0.93 RAPDs + AFLPs) indicate a good fit of respective clusters to genetic similarity data. The correlation of cluster analyses to pedigree information and the impact on parental genotype selection is discussed.

Genetic diversity and relationships among pea cultivars revealed by RAPDs and AFLPs

The bibliography presents 525 publications alphabetically by author on grain legume research in New Zealand covering the years 1910–2002. The index assigns entries by subject.

Bibliography of grain legume research in New Zealand 1910–2002

Sugarcane is an important international commodity as a valuable agricultural crop especially in tropical and subtropical countries. Two bulked DNA used to screen polymorphic primers from commercial hybrids (varieties) with moderately resistant and highly susceptible to red rot disease. Among 145 simple sequence repeat and unigene primers screened, 37 (25%) were found to be highly robust and polymorphic with Polymorphism Information Content values ranging from 0.50 to 1.00 with the mean value of 0.82. Among these microsatellites, twenty one were used in the study of genetic relationships and marker identification in sugarcane varieties for red rot resistance. A total of 105 polymorphic DNA bands were identified, with their fragment size ranging from 54 to 1,280 bp. Jaccard’s similarity coefficient value recorded between closely related hybrids was 0.986 while lowest coefficient value of 0.341 was detected with distantly related hybrids. The average similarity coefficient among these hybrids was 0.663. Cluster analysis resulted in a dendrogram with two major clusters separating the moderately resistant varieties from highly susceptible varieties. Three group specific fragments amplified by unigene Saccharum microsatellite primers viz; two markers UGSM316850 and UGSM31660 were closely associated with moderately resistant varieties by appearing bands in this region but the bands were absent in highly susceptible varieties. Similarly UGSM316400 marker was tightly linked with highly susceptible varieties by amplifying uniformly in sugarcane varieties showing highly susceptible reaction to red rot but it was absent in moderately resistant varietal groups. Validation of red rot resistance/susceptibility associated markers on a group of different mapping populations for red rot resistant/susceptible traits is in progress.

Genes tagging and molecular diversity of red rot susceptible/tolerant sugarcane hybrids using c-DNA and unigene derived markers

The pea (Pisum sativum L.) is an important agricultural plant with a rich history of genetic research. The development of ‘scientific’ breeding methodologies in the first half of the twentieth century was based partly on the application of genetic theory following the rediscovery of Mendel's Laws, but mostly on developing procedures for systematic phenotypic selection. During the last few decades, the use of molecular markers, revealing polymorphism at the DNA level, has been playing an increasing part in plant breeding. The development of high-density molecular maps which has been facilitated by PCR-based markers, have made the mapping and tagging of almost any trait possible. Marker-assisted selection has the potential to deploy favorable gene combinations for desirable trait. This review discusses the current use of available genetic marker technologies in pea breeding and provides an outlook for use of new technologies.

Molecular markers in pea breeding – a review

Garden pea (Pisum sativum L.), a member of the Fabaceae family, is one of the most important self-pollinating legume crops. Globally, the pea is an economic crop, utilized as food, feed and industrial uses. Garden pea is an annual winter-season crop grown around the world from winter to early summer depending on the country. Gene banks have conserved a large genetic resource collection of pea germplasm. Pisum harbors significant diversity based on biological status, geographical regions and morpho-agronomic traits. Introgression of novel alleles through crossing between various pea genetic resources, e.g. modern varieties with locally adapted varieties, enhances genetic diversity and preselection for traits of interest, which is required to ensure meaningful natural variation at the phenotypic level. Improving pea for biotic and abiotic stress tolerance traits, quality traits and yield attributes are the main objectives of breeders and geneticists. These can be achieved with genomics tools to augment traditional breeding programs. In this chapter, we will provide an overview of the origin of the pea, distribution, genetic resources, conservation, cultivation practices, recent developments in biotechnology and molecular genetics to improve traditional breeding methods.

Breeding Strategies of Garden Pea (Pisum sativum L.)

Introducing resistance genes through plant breeding remains an important and effective means of protecting plants from diseases. Plant species commonly carry genes for disease resistance within their collective germplasm base. Disease resistance can either be monogenic (ie. encoded by a single gene) or quantitative (ie. encoded by a number of genes). The first step in disease resistance breeding is to identify accessions carrying the resistance phenotype. The conventional process of breeding for resistance involves making controlled crosses and selecting sexual progeny for improved disease resistance. While relatively straight-forward for dominantly-inherited single gene resistance, this process becomes progressively more difficult and time-comsuming for resistance encoded by single genes with recessive inheritance and for quantitatively inherited resistance. Through the process of genetic linkage mapping, molecular markers which are linked to disease resistance genes can be identified, and these can then be applied in plant breeding programmes to assist in resistance gene introgression. Our research group has identified DNA tags for a number of genes for resistance to diseases affecting peas (Pisum sativum L.). For example, DNA markers linked to recessive genes for resistance to pea seed-borne mosaic virus (PSbMV) pathotype P-1 (Timmerman et al. 1993) and to powdery mildew fungus (Timmerman et al. 1994) have been identified. These genes are termed sbm-1 and er-1, respectively. In more recent research, we have identified markers linked to the dominantly inherited gene for resistance to pea enation mosaic virus (PEMV). This gene is termed En. The molecular markers linked to these three monogenic disease resistance genes have been applied in a field pea breeding programme to develop germplasm containing multiple disease resistance phenotypes. DNA tags linked to sbm-1 and er-1 have been used in conjunction with limited direct testing for disease resistance. Although widely distributed throughout the world, PEMV does not occur in New Zealand; therefore breeding for resistance to PEMV requires the use of overseas disease testing or DNA tags. The DNA tags linked to En have been used in the early stages of cultivar development without direct testing for disease resistance. The genes contributing to quantitatively inherited disease resistance can also be characterised using linkage maps and DNA markers and DNA tags can be developed (Michelmore 1995). Experiments to map the genes for resistance to Ascochyta blight of peas are currently underway, using a QTL mapping experimental design. Similar experiments have been carried out by our research group to map genes for two other quantitatively inherited traits, seed weight (Timmerman-Vaughan et al. 1996) and green seed colour (McCallum et al. 1997). Ascochyta blight is a serious disease of peas which is caused by a trio of fungal pathogens: Mycosphaerella pinodes, Ascochyta pisi and Phoma medicaginis. Accessions with improved resistance to Ascochyta blight have been identified among peas bred by the Crop & Food Research field pea breeding programme. Using these accessions as the resistant parents, large populations of F 2 progeny and their descendants have been developed. The genotypes of these segregating

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A.C. Russell

Papers

Dna markers for disease resistance breeding in peas (pisum sativum l.)