Fundamental studies on the analysis of genetic resources in sweetpea (Lathyrus odoratus L.) and their potential in breeding

The present study was conducted to analyze the genetic resources in sweet pea (Lathyrus odoratus L.) and to assess their potential in breeding with the objective of raising cultivars adapted to cut flower production in Japan. I first evaluated 35 morphological and culture characteristics in 38 cultivars. Based on the results obtained, the efficacy of 'tendril-less trait', as a labor-saving characteristic, was analyzed. To this end, two tendril-less cultivars were raised and their performance for cut flower production was tested. Furthermore, the genetic relationship among 87 sweet pea cultivars and two related species was investigated using amplified fragment length polymorphism (AFLP). The salient results of the study are summarized below: 1. Thirty-five morphological and culture characteristics were examined in 38 sweet pea cultivars. We analyzed the relationship between the characteristics, especially those deemed important for reducing labor costs, such as the tendril-less trait, and calculated their correlation coefficients. Cluster analysis, employed to evaluate the obtained dataset, revealed that 34 of the 38 tested cultivars could be classified into three clusters, namely Cluster I, II, and III. Cluster I cultivars could be recommended as garden-type plants because their initial flower buds were too late to be forced. Cluster II cultivars would be suitable as cut flower type plants, whereas Cluster III cultivars seemed to be appropriate as garden- or container-type plants because their flowers had very short peduncles, making their use as cut flowers, unsuitable. Furthermore, some factors, important for classification of the cultivars, were identified using the principal component analysis; these results were consistent with those of the cluster analysis. 2. Morphological characters of compound leaf were investigated using two tendril type cultivars and four cultivars and three lines of the tendril-less type. Compound leaf of the tendril type cultivars had one pair of leaflets with a tendril, whereas the tendril-less compound leaf was pinnate and had a few pairs of leaflets without the tendrils. In the case of tendril-less compound leaves, there were four differently shaped leaflets including a fibrous leaflet, a rudimentary organ without the leaflet, those with a pinna beside the normal leaflet, and a compound leaf with or without a terminal leaflet. The characteristics of compound leaf in the tendril-less type cultivars were different. Leaf area of the tendril-less type cultivars was not necessarily greater than that of the tendril type ones. Leaf length, leaf width, peduncle length, first leaflet length, and first leaflet width were identified as important parameters of leaf area and were also useful in selecting the tendril-less type cultivars that are able to set in dense planting. 3. Two new tendril-less cut flower cultivars, 'Musica rose' and 'Musica purple', were bred using three cultivars and were classified based on the culture characteristics described in chapter 1. Their labor saving effects were also investigated. These cultivars were derived from crosses between the tendril-less and tendril type cultivars. Because the tendril-less trait is recessive, it was selected in the Fsub(2) generation and fixed in the Fsub(3) generation. 'Musica rose' is a spring-flowering-type cultivar, having strong purplish-pink flowers with a large diameter, whereas 'Musica purple' is a winter-flowering-type cultivar with vivid reddish purple flowers with a medium diameter. Although, 'Musica purple' is a winter-flowering-type cultivar, it is possible to cultivate it as a spring-flowering-type cultivar in a forced culture. Under routine training, the operation times to take off all tendrils at each leaf and all lateral shoots at each node for the two new tendril-less cultivars were less than half of that for the normal tendril cultivars. Furthermore, the results of motion analysis suggested that the required angles of movement of a worker's elbows and wrists were narrower and the distances of elbow movements were shorter for the tendril-less cultivars than for the tendril type cultivars. These results suggested that the tendril-less cultivars could improve labor productivity and reduce the load of workers. 4. To obtain knowledge for the selection of breeding materials, genetic relationships among 87 sweet pea cultivars and two related species were assessed using AFLP. Based on the results obtained, the sweet pea cultivars were grouped into two clusters. Cluster I consisted of four cultivars. It included a wild cultivar, 'Cupani' and cultivars established from spontaneous mutation or natural hybridization, such as 'Cupid' and 'Painted Lady'. The bigger cluster, Cluster II, consisted of 83 sweet pea cultivars. There was no distinct subcluster in the cluster II that shared the common morphological or ecological characteristics, such as the tendril-less trait, plant type, or flowering habit. The distinct genetic differentiation among the cultivars most likely seemed to reflect that the sweetpea breeding originated in the United Kingdom, 300 years ago, with limited genetic resources. The two species related to sweetpea, L. belinensis and L. chloranthus, formed an out-group, which was designated as Cluster III. These species have yellow-colored flower that are absent in sweetpea and report the success of interspecific hybridizations. Thus, hybridization with genetically distinct, exotic resources might contribute to the development of new sweetpea cultivars. Furthermore, AFLP technique proved to be a reliable tool for cultivar identification, for determining the genetic relationships among the sweetpea cultivars and related species, and for use as a marker in linkage analysis. In the present study, many characteristics were analyzed to raise sweetpea cultivars adapted to cut flower production in Japan. Based on the evaluation of the characteristics, two tendril-less cultivars were raised and assessed for cut flower production. Genetic relationships among the sweetpea cultivars and related species were revealed by AFLP analysis. The results obtained in the present study have great potential in improving sweetpea breeding.