蕹菜遺傳歧異性及白

Abstract

台灣蕹菜栽培品種(系)名稱甚為混雜，高溫多溼環境下易引起白

Water spinach (Ipomoea aquatica Forsk.) is an important summer vegetable in Taiwan, and most of the cultivar/lines are not resistant to white rust disease especially growing under high humidity and high temperature. Besides, the varieties (lines) of water spinach (Ipomoea aquatica Forsk.) were not clearly classified in Taiwan. The objective of this study was to identify the genetic relationship among the 41 water spinach accessions through numerical analysis of the vegetative characters in the juvenile stage and to estimate the resistance/susceptibility to white rust disease. The vegetative characters investigated were leaf color, shoot length of cotyledon stage, node number of cotyledon stage, shoot length of leaf stage, node number of leaf stage, shoot length of sowing after 35 days, node number of sowing after 35 days, leaf length, leaf width, leaf length/leaf width, cotyledon length, cotyledon width, cotyledon length/cotyledon width, relative shoot biomass, relative leaf length biomass, relative leaf width biomass, relative node number biomass, internodes length. Using cluster analysis of the 17 vegetative characters, 41 accessions were divided into four main groups, and the accessions within groups displayed diversity; besides, the first three groups clustered together before they clustered with the forth group. The first group (I) included the accessions such as ‘Pyng Dong Da Yeh’ line with the morphology as big cotyledon (both width and length), tall and straight plant type, dark-green plant color, and lanceolate leaf shape. Accessions in the second group (II) were plants shorter than those in the first group with light green plant color, short internodes, hastate or long ovate leaf shape, such as ‘Bair Ku Ching Yeh’ line. The plant types of the third group (III) were dark-green color, and ovate leaf shape, such as ‘Jwu Mu Dan’ line. The plants of the forth group (IV) were shortest and yellow-green with cordate leaf shape, such as ‘Bair Ku’. The ordination pattern of the principal component analysis was similar to the grouping pattern of the cluster analysis, and the first three principal components derived form the principal component analysis explained 72.37% of the observed variation. The 10 ‘Bair Ku’ accessions were distributed into two groups, II and IV. As we analyzed the 10 accessions by the principal component analysis on the basis of the 17 characters, the first three principal components derived from the principal component analysis explained 88.7% of the observed variation and four characters were selected as principle components. The four characters were shoot length, cotyledon length/cotyledon wide, relative shoot biomass and leaf length. The dendrogram derived from the four characters resembled that derived from 17 vegetative characters. The disease rating among the accessions were significant different and were divided into 6 grades. Accession with grade 0.01-1 was referred to the tolerant lines such as ‘Pyng Dong Dah Yeh’, accession with grade 1.01-2 was referred to the susceptible lines such as ‘Taoyuan No. 1’, whereas accession with grade 2.01-4 was referred to moderate susceptible lines such as ‘Jwu Mu Dan 99'’. Most of the accessions tested in this study were tolerant to moderate susceptible. Results of disease ratings and cluster analysis among accessions were not related. The tolerant of accessions were ‘Jwu yeh’, ‘CV6 99'’, ‘7-4 Bair Ku Ching Yeh’, ‘Bair Ku Ching Yeh-2 8-2(2)’, ‘4M Yo 2 38’, ‘Bair A1’, ‘Ywu Dan 1-2(2)’. Those accessions diverted in different groups. Besides, a significant influence of different Albugo source to water spinach was also concluded. Soil from Albugo infected field was collected and tested. Soil from ‘Taichung’ and ‘Composite’ resulted in the most severe ratings. However, all the disease symptoms were the same. The infection of white rust disease caused the decrease of total chlorophyll content. ‘Jwu Mu Dan 99'’, a susceptible line, reduced 53%; however, there was no significant difference in chlorophyll content was observed in tolerant lines such as ‘Bair A1’ and ‘Ywu Dan 1-2(2)’ and ‘Jwu yeh’. The symptoms of the infected leaves of ‘Jwu yeh’ and ‘Ywu Dan 1-2(2)’ contained yellow halos on the upper (adaxial) epidermis and underneath white pustules on the lower (abaxial) epidermis, but that of ‘Bair-A1’ infected leaves only had yellow halos on it. This finding indicated difference resistance mechanism involved in these two tolerant lines. The decreased of chlorophyll content and disease ratings were positive correlated suggested that the content of chlorophyll could be a resistance indicator when water spinach infected with white rust disease.