Intergeneric hybrids of Saccharum.
AbstractGlagah, the Javanese variety of S. spontaneum, with 2n = 112 chromosomes was crossed with Erianthus ravennae (2n = 20 + a fragment) and the F1 and F2 generations were studied. The F1 had more resemblance to S. spontaneum and was found to have 66 chromosomes (56 + 10) in the root tips. At meiosis it formed univalents, bivalents, trivalents and quadrivalents; it was inferred that autosyndesis occurred among the S. spontaneum chromosomes and that some of the Erianthus chromosomes were capable of pairing with S. spontaneum chromosomes.
As would be expected from the irregularities at meiosis in F1 the chromosome numbers in F2 were variable. The seedlings studied cytologically fell into three groups, the largest group being approximately diploid, with 68 to 76 chromosomes. There were also three hypotriploids with 104, 106 and 108 chromosomes and one hypertetraploid with 136. The diploids showed segregation of the Erianthus characters presence of awn and compound inflorescence and a unimodal distribution in respect of the proportion of the length of the callus hairs to the length of the glumes. The triploid and tetraploid seedlings had thicker stems, wider leaves and a larger inflorescence than the diploids. The sugar content of the diploids was considerably less than that of the Saccharum parent, that of the triploids and tetraploids slightly so.
Quadrivalents and many univalents were observed at meiosis in the diploid F2 hybrids and the division was more irregular than in the tetraploid, where a few quadrivalents and even sexivalents were found.
Among the seedlings obtained by pollinating an arrow of P.O.J.2725 (2n = 106) with Imperata cylindrical (2n = 20), four types occurred. There were two apomictic seedlings with 2n = 106, resembling P.O.J.2725 closely in habit and having the same pollen fertility (23-35%), six seedlings produced by selfing or diploid parthenogenesis, with 108-112 chromosomes and little or no pollen fertility, a triploid self which had 156 chromosomes and failed to flower and five true hybrids with 120 to 134 chromosomes, representing approximately the diploid complement of the Saccharum parent with the haploid complement of I. cylindrica.
The true hybrids resembled sugar canes very closely and had a high pollen fertility (50 to 80%). At meiosis bivalents and a variable number of univalents were found. An F2 was raised from a plant with 80% pollen fertility and segregation of Imperata characters was observed. Some F1 seedlings obtained from this cross had sugar contents nearly as high as P.O.J.2725.
The noble sugar cane Vellai (= Lahaina) with 2n = 80 chromosomes was crossed with the sweet corn Golden Beauty, 2n = 20 + 2B chromosomes. Two seedlings were obtained of which one survived and was found to have 52 chromosomes. It is suggested that the cross is difficult because of the relatively low sugar concentration required for the germination of maize pollen. The hybrid is a dwarf, tillers freely, is perennial and can be propagated vegetatively. It shows no sign of flowering. The upper surface of the leaf bears long silky hairs similar to but larger than those in maize. The only other Saccharum with this character is the freak cane Troeboe, of Java and the author suggests that the latter may be derived from a cross of Saccharum with a member of the Maydeae.
In view of the crossability of the highly polyploid Saccharum species, the fertility of their progeny and the versatility of their reproduction, the author points out that there exists a vast field of hybridization work which has yet to be explored.