CHROMOSOME TRANSMISSION AND MEIOTIC STABILITY OF SUGARCANE (SACCHARUM SPP) HYBRID DERIVATIVES

Efficiency of selection in sugarcane (Saccharum spp. hybrids) breeding may be influenced by the type of chromosome transmission. Our objectives were to determine chromosome transmission and meiotic stability among and within sugarcane families derived from crosses of elite, interspecific clones with four S. spontaneum L. clones. The cytological behavior, pollen stainability, and seed yield were measured for 23 nonrecurrent clones in parental, F1, and BC2 to BC3 generations. Chromosome number was determined for 13 recurrent parents. Chromosome transmission was strictly n + n, although meiotic irregularity, aneuploidy, and chromosomal mosaicism resulted in aneuploid gametes. Chromosome number increased quadratically with generations from 2n = 60.5 in S. spontaneum parents to 2n = 84.0 at F1, 97.5 at BC1, 106.1 at BC2, and 108.0 at BC3. Chromosomes paired primarily as bivalents, although variable numbers of univalents and multivalents were observed. The frequency of trivalents increased linearly with generations, and was greater in hybrid derivatives than in parental S. spontaneum clones. Multivalent pairing indicated that autosyndesis was incomplete. Meiotic irregularities also included multiple nucleoli, anaphase bridges and laggards, asynchronous meiosis, chromosome fragments, pseudobivalents, first and second division restitution nuclei, and syncytes. One clone, 'CP 33-224', was partially desynaptic. Results suggest that sugarcane cultivars and S. spontaneum share a common endosperm balance number unlike S. officinarum L. and S. spontaneum. Transmission by n + n may indicate that additional cycles of random mating among hybrid derivatives, relative to that with 2n + n transmission, may be necessary to recover desirable recombinants in sugarcane populations.