TARO BREEDING IN INDIA M.T. SREEKUMARI, K. ABRAHAM AND M. UNNIKRISHNAN CENTRAL TUBER CROPS RESEARCH INSTITUTE,TRIVANDRUM - 695 017, INDIA ABSTRACT The genetic improvement of taro (Colocasia esculenta (L.) Schott) is one of the major research programmes of the Central Tuber Crops Research Institute, Trivandrum, which maintains 424 edible accessions. Field evaluation of 369 accessions resulted in the identification and release of two high yielding superior varieties from the CTCRI Headquarters at Trivandrum and a leaf blight tolerant type from its Regional Centre at Bhubaneswar. The varieties developed from germplam selections are triploids indicating the higher yielding potential of triploid taros than diploid taros. By intervarietal hybridization in diploid taros, a large number of hybrids were produced from different combinations. Of the 4280 sergeants evaluated, 802 (18.7%) were rated as above average for important attributes like dwarf plant types, higher corm and cormel yield, non-acridity, long keeping quality and early maturity. From the initially screened segregants, rigorous selection for the above attributes resulted in the identification of seven superior hybrids viz., H-2, H-3, H-4, H-12, H-13, H-120 and H-160. They consistently recorded higher tuber yields and superior quality attributes during the yield trials at the CTCRI. Currently they are being evaluated in farmers’ fields for verification of their merits, prior to variety release. Besides the above high yielders novel types like dwarfs, erect types, profusely flowering lines and CLB tolerant types were identified among the segregants. With the regular flowering of the clones and the possibility of producing full sibs, half sibs and selfs, taro breeding has been pursued at the CTCRI extensively and intensively, for developing hybrid varieties combining the various superior attributes. The latest approach in taro breeding at the CTCRI is to artificially produce triploids by crossing diploids with induced tetraploids to increase productivity. For this, tetraploid taros developed by colchicine treatment are being tested for flowering, fertility, and interploid (diploid x tetraploid) compatibility for the production of triploids. Introduction Colocasia esculetna (L.) Schott) is a popular tuber crop consumed as a vegetable in India and South East Asia while it is an important staple food in the Pacific region. It is commonly known as taro, dasheen, cocoyam and occasionally eddoe. It belongs to the family Araceae. Despite its importance as a popular edible tuber crop, very little attention has been devoted to the genetic improvement of taro. Great back of the research work on taro has been chromosome studies (Yen and Wheeler, 1968; Vijaya Bai et al., 1988; Coates et al., 1988; Sreekumari and Mathew, 1991 a, b). Information on the sexual potentialities of the crop has been very fragmentary, and the improvement programme have been largely dependent on the 1 exploitation of the existing genetic variability among the cultivars (Warid, 1970; Kuruvilla and Singh, 1981, Plurre, 1984; Tanimoto and Matsumoto, 1986; Velayudhan and Muraleedharan, 1987; Singh and Singh, 1987; Unnikrishnan et al., 1987; 1988; Lebot and Aradhya, 1991). For a long time it was believed that taro plants do not flower, and therefore fail to produce seeds (Kikuta et al., 1938; Plucknett et al., 1970; Shaw, 1975). However, later reports from different countries indicate that many clones flower and produce viable seeds (Abraham and Ramachandran, 1960; Plucknett et al., 1970; Shaw, 1975, 1984; Jackson et al., 1976, Jos and Vijaya Bai, 1977; Strauss et al., 1980; Ghani, 1984). Because of its long history as a cultivated crop and of the vegetative mode of propagation, it has been possible to select and preserve distinct types or varieties in taro, which are useful to man. Accumulation of such multiplicity of types must have made it possible for suitable cultivars to be selected in different areas and in various growing conditions of soil, water, altitude, temperature, planting practices, etc. Doku (1980) has pointed out that this large store of variation present in the crop would be immediately available for utilization in the raw state and in all future combinations and recombination if conditions for flowering, hybridization, seed setting and raising of seedlings are discovered. Research Priorities for Taro Genetic Improvement: - - Germplasm collection, maintenance, characterization and evaluation - Publishing bulletins and catalogues for easy reference - Evaluation of the collections and identification of suitable cultivars for (1) direct release based on performance in the different field trials conducted at the Institute farm and in on farm trials (2) incorporate in various breeding programmes - Intervarietal hybridization and production of true seeds - Production of selfed seeds - Evaluation of the seedling and subsequent clonal progeny for various desirable attributes - Identification and multiplication of the selected hybrids for the conduct of field trials - Isolation of superior hybrid selections for release - Production of triploids in large scale by crossing induced tetraploids with diploids - Evaluation of the induced triploids and identification of genetically improved types. The Taro gene bank The taro gene bank at the CTCRI possesses 424 accessions collected from all over India. The cormels are planted in April-May and harvested after six months. Important characters were recorded 2 based on modified IPGRI descriptor and catalogues and bulletins were published. (Unnikrishnan et al., 1987). A wide spectrum of genetic variability was noticed among them for several characters, especially growth habit, pigmentation on different plant parts, crop duration, flowering habit, fertility, open pollinated fruit and seed set, size, shape and yield of corm and cormels, cooking quality, tolerance to leaf blight disease etc. Evaluation trials were undertaken such as row trials, preliminary evaluation trials, advanced yield trials and finally on farm trials prior to the release of superior selections. Two accessions viz. C.149 and C.266 were thus released for general cultivation under the names Sree Reshmi and Sree Pallavi respectively from the CTCRI. A gist of the characters of these two varieties and few of the elite germplasm collections identified are given in the Table1 Table 1. Important characters of the released varieties and other elite germplasm selections Germplasm selections Description 1. C.149 (Sree Reshmi) This is a local collection and is a natural triploid. It grows to a height of 1-1.5 m and has edible petiole, leaves, corms and cormels . Cooking quality is excellent. It matures in 7-8 months and cormel yield ranges from 15-19 t ha-1. Cormels contain 14-16 percent starch and 2-2.5 per cent protein. This was released from the CTCRI during 1987. 2. C-266 (Sree Pallavi) It is another released variety of taro from the CTCRI. It is a triploid collection from Meghalaya. Plant height ranges from 1-1.5 m and the crop duration is 7-8 months with a yield potential of 12-15 t ha-1. Only the cormels are edible. The starch content ranges from 19-23 per cent and protein content 1.8-2.1 per cent. 3. C-9 A triploid accession. It is an early maturing type (5-6 months) with medium height (60-80 cm). The leaves are medium broad and average yield (cormel yield) is 15 tonnes per hectare. Cormels are excellent for culinary purpose but the cormel keeping quality is poor. 4. C-189 It is a high yield triploid with an average yield of 20 t ha-1. The plants are tall types with comparatively long duration. The cormels are many and long fusiform in shape. The most 3 attractive attribute of this selection is the long keeping quality of the cromels (4-5 months) 5. C-303 and C-384 These two diploid accessions are the only ones in the germplasm that flower almost regularly. The flowers are highly fertile resulting in open pollinated seed production The plants are of medium type, cormel yield ranges from 10-14 t ha-1 and cooking quality is good. Both the accessions are usually incorporated in the breeding programme. 6. C-408, C-444/2 and C-481 These accessions are tall, late maturing types. They produce comparatively large main corm (> 500 g) with 8-10 well-developed big cormels. They are identified as triploids, but based on tuber characters they can be treated as ‘intermediate types’ between dasheen and eddoe groups. Ploidy in relation to tuber yield Twenty diploids and twenty triploids were evaluated for growth performance and yield. It was observed that triploids are superior to diploids in seven of the nine characters studied. The corm and cormel yield showed very promising and impressive increase in the triploids except in the case of cormel number which was significantly more in diploid plants.. This implies that for selecting high yielding types in taro it is desirable to consider the triploids rather than diploids. The comparative performance and extent of variability noticed within the two ploidy types is given in Table 2. Table 2. Comparative performance of diploid and triploid taro Sl. Characters Diploids Triploid t value No. Mean CV (%) Mean CV (%) 1 Plant height (cm) 69.7 ± 0.47 33.14 76.3 ± 2.2 31.6 2.168* 2 Tiller number 3.4 ± 0.14 44.12 3.6 ± 0.17 52.8 NS 4 1.090 3 Number of leaves 8.3 ± 0.56 73.49 8.1 ± 2.22 60.49 NS 6.276 4 Shoot girth (cm) 8.8 ± 0.79 98.86 14.6 ± 0.46 34.93 6.149** 5 Leaf length (cm) 20.5 ± 0.84 44.87 30.4 ± 0.58 21.05 9.628** 6 Leaf breadth (cm) 16.0 ± 0.67 45.63 25.4 ± 0.56 24.02 10.823** 7 Corm weight (g) 141.2 ± 8.01 62.11 203.6 ± 10.94 58.59 4.600** 8 Cormel Number 18.8 ± 1.00 65.48 12.6 ± 0.70 60.16 3.050** 9 Cormel weight (g) 206.2 ± 7.69 40.88 447.1 ± 8.03 26.51 6.348** *Significant at 5% level ** Significant at 1% level NS -Not significant Flowering frequency and floral biology: - Flowering was seasonal mostly starting by the middle of June (2-3 months after planting) and lasting till the middle of September.