Rodomiro Ortiz, Piers D. Austin and Dirk Vuylsteke
A. Tenkouano, J.H. Crouch, H.K. Crouch and D. Vuylsteke
We attempted to determine ploidy level in the gametophyte and the sporophyte of Musa using pollen and chloroplast characteristics, respectively. In the gametophyte, interploidy differences accounted for 63.8% of the genetic variance for pollen diameter and 87.5% for pollen stainability, the remainder being attributable to intraploidy differences among clones. While pollen count and stainability effectively separated triploid accessions from diploids or tetraploids, they did not discriminate between diploids and tetraploids. In the sporophyte, the relative contributions of interploidy and intraploidy differences to genetic variation in the number of chloroplasts in stomatal guard cells were 70.8% and 29.2%, respectively. Although pollen diameter and chloroplast number increased with ploidy, the use of the sporophytic parameter appears to provide a more satisfactory means of estimating ploidy status in Musa.
J.B. Hartman, D. Vuylsteke, D. Makumbi, R.N. Ssebulibe and D.A. Karamura
The East African highland bananas are a sub-group of the Musa AAA group and are unique to the mid-altitude and highlands of Eastern Africa. In much of the area where they are grown, highland bananas are the main staple crop for both rural and urban populations. Yields of highland bananas have fallen precipitously in many areas and production deficits have been met by shifting highland banana production into new areas. Yield reductions have been attributed to a number of factors, including plant parasitic nematodes, the banana weevil (Cosmopolites sordidus), and black Sigatoka leaf streak (Mycosphaerella fijiensis). A program to breed improved highland bananas was established at the International Institute of Tropical Agriculture's Eastern and Southern Africa Regional Center (IITA-ESARC) in collaboration with the National Banana Program of Uganda in 1994. Following preliminary studies of fertility, breeding began in 1997. The breeding program has taken as its model IITA's successful plantain-breeding program. The plantain-breeding program has used an ideotype breeding approach to selection of improved plantain hybrids. The unique features, culture, and end-use of highland bananas have necessitated the definition of a new ideotype. Results of studies during the past 2 years have identified traits unique to highland bananas and a highland banana ideotype has emerged.