Research Journal of Agriculture and Biological Sciences, 34(): 264-266, 2007 © 2007, INSInet Publication Corresponding Author: S. Muthulakshmi, Department of Fruit crops, Horticultural College and Research Institute, Tamil Nadu Agricultural University, Coimbatore – 641 003, Tamil Nadu, India. 264 Breeding for Cold Tolerance in Papaya (Carica papaya L.) Through Hybridization S. Muthulakshmi, T.N. Balamohan, R. Amutha, W. Baby Rani , P. Mareeswari and K. Indira Department of Fruit Crops, Horticultural College and Research Institute, Tamil Nadu Agricultural University, Coimbatore – 641 003, Tamil Nadu, India. Abstract: Crossing was undertaken using papaya variety CO 2 (Carica papaya ), as female and mountain 1 2 papaya (Carica candamarcensis), as male. Their F and F progenies were evaluated for tolerance to cold. 1 The mean performance of F progenies for plant height, petiole length, leaf area and number of leaves at first flowering, average fruit weight, fruit number, fruit length, fruit circumference, fruit volume, cavity volume, pulp thickness, TSS and fruit yield per tree were found to be lower than the better parent 2 CO 2. Variability was observed in F population for the morphological, physiological and biochemical characters. Clustering analysis with KMEANS joining algorithm was also performed to narrow down 2 the F population and found that genotypes G 15, G 22 and G 27 were found to be different from the rest. 1 2 Key words: Papaya variety CO 2, Carica papaya, Carica candamarcensis, F and F progenies, KMEANS joining algorithm INTRODUCTION Papaya (Carica papaya L.) is one of the important tropical fruit crops. The fruits are rich in vitamin 'A' (2020 IU) and vitamin C (46 g). Latex is extracted from unripe papaya, which has many pharmaceutical and cosmetic applications. Papaya cultivation has many hurdles like dioecious nature, susceptibility to water logging, low temperature, papaya ring spot virus (PRSV) and leaf curl virus. Among the various problems, low temperature is one of the most important environmental factors, which affect the plant growth and productivity. Hence this study was undertaken, with the objectives of to introgress cold tolerance gene into cultivated type and to develop a cold tolerant gynodioecious papaya for table purpose. MATERIALS AND METHODS Research was carried out at Horticultural College and Research Institute, Tamil Nadu Agricultural University, Coimbatore during 2003-2006 to develop a cold tolerant gynodioecious papaya line. The dioecious variety of papaya CO 2 was crossed with its wild relative carica candamarcensis. Seeds were collected from the crossed fruits and sown in nursery for raising 1 F population. A total of 107 seedlings were raised in 1 F . Among the total population, 52 hermaphrodite and 55 female plants were observed. Morphological, yield and quality characters were 1 1 recorded in F population. In F hermaphrodite plants were given importance because of difficulties in maintaining purity in female plants through crossing. Best performed progenies based on morphological, yield and quality characters were selected and selfed. 2 The F population was raised at Horticultural Research Station, Thadiyankudisai, at a higher elevation of 1100 2 m MSL. In F population, morphological characters were recorded at 9 month after planting. Samples th 2 were collected from all the F plants and physiological and biochemical characters related to cold tolerance were analyzed. RESULTS AND DISCUSSIONS 1 The mean values of F hermaphrodite plants for morphological characters were given in Table 1. The 1 mean value of hermaphrodite F plants was lower than the parents and this is a desirable character with regard to papaya. First bearing height and plant stem girth at first flowering had higher mean values than the parents. The other morphological characters including yield attributes were having lower mean values than the parents. This might be due to the wild male parent carica candamarcensis. Mean value is used as a 1 primary criterion for selection in F population. From 1 the F population based on higher mean values, eight elite hermaphrodite plants were selected and forwarded 2 to F population. In general morphological characters were lower 1 than F population and parents. Generally low temperature delays the growth and development of plants. This might be the possible reason for low mean 2 values of morphological characters in F population. 2 Leaf samples were collected from all the F plants and physiological and biochemical characters