Morphology and cytology of a novel intergeneric hybrid Saccharum x Tripsacum and its derivatives

The present day commercial sugarcane varieties are derivatives of man made interspecific hybrids between cultivated Saccharum officinarum and wild S. spontaneum of the family Gramineae. Interspecific and intergeneric hybrids with wild related species are being developed for the genetic base broadening of sugarcane. The present study is on the morphology and cytology of a novel hybrid between sugarcane and Tripsacum, a robust perennial grass native of the western hemisphere. The sugarcane variety CoC671 (2n= 108) when pollinated with Tripsacum sps. hybrid (2n= 54) gave rise to hybrids with chromosome number ranging from 2n= 108 to 116 and resembling sugarcane in morphology. In pollen mother cells there were predominance of bivalents and a few multivalents at metaphase I, meiotic abnormalities such as lagging chromosomes and disoriented spindles in anaphase I and asynchronous division and disoriented spindles in anaphase II. These hybrids were fertile and were further crossed with sugarcane and Tripsacum to obtain backcross progeny. The Saccharum x Tripsacum hybrid backcrossed with the sugarcane variety Co 775 gave rise to two distinct morphological categories of plants, one with high tillering (Mean = 41) and thin canes (1.44 cm) and another with low tillering (13.39) and thick canes (2.39 cm). Their leaf width also varied significantly. Most of the broad leaved plants were non-flowering. The back cross hybrids with Tripsacum were with less cane height and with broad and long leaves. Among the backcross hybrids a few plants had the Tripsacum morphological features on leaf and stem. The inflorescence of all the hybrids had resemblance with that of Saccharum. Fertility of the hybrids and variability in the backcross progeny had shown that these hybrids can be further used in genetic base broadening of sugarcane. INTRODUCTION Sugarcane is an important agro industrial crop of tropical and subtropical regions and is cultivated on close to 20 million hectares in more than 90 countries. Sugarcane belongs to the grass family (Gramineae), an economically important seed plant family that includes cereals such as maize, wheat, rice, and sorghum as well as many forage crops. The modern commercial cultivars of sugarcane are interspecific hybrids between cultivated Saccharum officinarum and wild S. spontaneum. In order to widen the genetic base for its diversified use for production of sugar, ethanol, fibre and electricity and to improve the productivity interspecific and intergeneric hybridization with wild related species is being performed (Sreenivasan et al., 1987). Intergeneric hybrids between Saccharum with members of Gramineae such as Erianthus (Janaki Ammal, 1941; D’Hont et al., 1995; Premachandran and Lalitha, 2007), Imperata (Janaki Ammal, 1941), Miscanthus (Li et al., 1948), Bambusa (Venkatraman, 1937), Sorghum (Thomas and Venkatraman 1930; Nair, 1999), Zea (Janaki Ammal, 1938) have been reported. The wide hybrids in sugarcane can be maintained by clonal propagation and due to the high ploidy level many of the hybrids are fertile also, thereby it can be used in gene introgression studies. Tripsacum is a perennial grass native to the western hemisphere, belonging to the Maydeae sub tribe of Andropogoneae tribe, closely related to Zea mays. The Tripsacum species are with predominantly diploid (2n = 2x = 36) or tetraploid (2n = 4x = 72) ploidy levels. The diploids reproduce sexually whereas tetraploids reproduce by diplosporous apomixis. Sexual allotriploids (2n =3x=54) were also developed from crosses of sexual diploid Tripsacum dactyloides (2n = 36), and apomictic tetraploid (2n = 72) T. maizar (Li et al, 2000). The present study is on the hybrid between a commercial sugarcane variety (Saccharum spp. hybrid) and the triploid Tripsacum species hybrid. MATERIALS AND METHOD The plant materials used in this study consist of sugar cane commercial varieties CoC 671 and Co 775 and Tripsacum sps. hybrid being maintained at Sugarcane Breeding Institute, Coimbatore which was originally received from Genetics Division, Indian Agricultural Research Institute, New Delhi. The inflorescence of field grown sugarcane variety CoC 671 was covered with a cloth bag before the start of spikelet opening and was pollinated with Tripsacum pollen for five days from the start of spikelet opening. The seedlings were raised in the glass house and were transplanted to poly bags after 25 days. These seedlings were transferred to field after 45 days. The hybrids obtained were pollinated with the sugarcane variety Co 775 or was selfed and seedlings were raised. One of the