Conventional Sugarcane Breeding in South Africa: Progress and Future Prospects

Initial sugarcane production in South Africa relied on imported varieties. When imported varieties succumbed to diseases, the industry established the South African Research Institute (SASRI) with the mandate to develop sugarcane varieties. The popular and highly successful varieties, NCo310 and NCo376 were selected from crosses imported from India. NCo310 and NCo376 were grown successfully in several countries across the world where they produced high yield and ratooning ability. Later, crossing was established at SASRI based on flowers initiated in the glasshouse and photoperiod house under controlled temperature and photoperiod conditions. A five stage program is currently being implemented in the variety development process. More than 60 varieties have been released from the breeding programs. Other achievements include development of germplasm that is currently being used to enhance sugar cane variety development in South Africa. Currently, high realised selection gains are evident in most of the advanced selection populations. The released varieties show genetic gains over time. Efforts to enhance the breeding program include introgression, family evaluation, selection models and use of molecular markers.

Selection for Eldana saccharina Borer Resistance in Early Stages of Sugarcane Breeding in South Africa

Eldana saccharina (eldana) is the most wide-spread sugarcane borer in South Africa and causes losses estimated at US$90 million. Breeding for resistance started in 1980. The objectives of this study were to examine the potential of evaluating sugarcane families and parents by using data collected from the seedling stage (Stage I) and determine the potential of using logistic regression models in Stage II to enhance breeding for eldana resistance. Data were collected from Stage I trials (BML12 and FML13) at Bruyns Hill and Pongola research stations, respectively, and Stage II (BSL12 and SSL12) at Bruyns Hill and Glenside research stations, respectively. There were significant family effects for BML12 (P = 0.0029) and FML13 (P = 0.0003) indicating families with low eldana dame could be selected. Family variance for BML12 (P = 0.0144) and FML13 (P = 0.0878) were significant indicating large variability. Broad sense heritability of 0.52 (BML12) and 0.51 (FML13) indicated the effectiveness of selecting elite families. The predicted gains were 19.93% (BSL12) and 68.89% (FML13) indicating the value of family selection. The results showed significant female effects (BML12, P = 0.0017;FML13, P = 0.0041) indicating the dominance of maternal effects and suggested additive genetic control. Significant Female x Male interaction effect (FML13, P = 0.0442) suggested existence of non-additive genetic effects. Logistic regression analysis results showed significant (BSL12, P < 0.0001;SSL12, P = 0.0232) suggesting selecting for eldana was effective. Sensitivity analysis validated discriminating ability for eldana damage. Adopting family selection and logistic regression models would enhance breeding for eldana resistance.

Whole-population Mapping of Sugarcane Germplasm Using Linkage Disequilibrium

Commercially grown sugarcane cultivars are advanced generation hybrids between two polyploid ancestor species, S. off icinarum L. (x=10, 2n=8x=80) and S. spontaneum (x= 8, 2n=5-16x=40-128). Modern cultivars

Simultaneous Selection for Yield and Stability in Sugarcane Using Parametric Statistics

Sugarcane advanced variety trials are planted across several locations and harvested for several crop-years to determine genotype by environment interaction and yield stability. Previous studies describe methods for simultaneous screening for yield and stability but did not use parametric statistical tests for comparing genotypes. The objective of this study was to describe a parametric statistical method for simultaneous screening of sugarcane genotypes for yield and stability. Data from 26 crops were collected from trials established at five locations and harvested in the plant, first, second, third and fourth ratoon crops. The mixed procedure of SAS was used for data analysis. The intercept and slope were used to represent yield and stability, respectively. There were significant （P 〈 0.05） differences in yield and stability among the genotypes. Test genotypes were classified into groups of genotypes that produced high yield, or high stability or both. The method provides fast statistical tests for simultaneous screening for yield and stability. The method was also used to compare two genotypes, an application for variety choice at time of release.

Molecular Markers Associated with Starch Content and Implications for Sugarcane Introgression Breeding Using Saccharum spontaneum

Introgression with Saceharum spontaneum intended to broaden the genetic base of sugarcane resulted in an increase in desirable genes for broader adapt ability as well as undesirable genes for high starch content. Markers could provide a quick and efficient method of screening parental genotypes for low starch. The objectives of this study were to identify potential markers associated with starch in S. spontaneum population and evaluate their potential for screening for starch content. Data for starch content and （simple sequence repeats） SSR markers were collected from 51 S. spontaneum clones grown in replicated pots. The mixed procedure of statistical analysis system （SAS） was used to determine markers significantly associated with starch. Thirty-nine out of 357 polymorphic markers were significantly （P 〈 0.05） associated with starch content. Eighteen were positively associated and 21 were negatively associated. The presence of a positive marker produced 39% more starch than absence while the absence of a negative marker produced 57% more starch than presence. Selecting parents using negative markers may be more efficient than selecting using positive markers.

Family Selection as a Strategy for Stem Borer (Eldana Saccharina Lepidoptera: Pyralidae) Resistance Breeding in South Africa

Eldana saccharina is the most damaging stem borer of sugarcane in South Africa causing US$90 million losses of revenue annually. The breeding strategy at the South African Sugarcane Research Institute is based on evaluating parents for breeding values using progeny data derived from family plots and selecting parents with high breeding values for crossing. Family selection entails selecting whole populations of progenies based on family mean. The objective of this study was to evaluate the contribution of family selection to eldana resistance breeding. Data were collected from stage 1 (seedlings stage) trials. In each plot, stalks were examined for eldana entry and exit holes and stalks with borings were counted. The number of bored stalks was expressed as a percent of total stalks and subjected to analysis of variance. The family broad sense heritabilities ranged from 0.51 - 0.56 compared with 0.17 for Individual Genotype Selection (IGS). Predicted family selection gains ranged from 20% to 69% compared with 18% for IGS indicating the value of family selection. Female parental effects F-values (1.63 - 2.01) were significant (P = 0.0017 - 0.0041) compared with non-significant male F-values (1.33 - 1.41) and (P = 0.088 - 0.1464) suggesting maternal effects. Crossing parents with higher resistance such as 96M0058 × 94M0017, 87M0965 × 98G1166 and 97M0653 × 94M0017 produced significantly (P < 0.05) fewer bored stalks compared with those showing lower resistance (96H0590 × 95H0167, 94F2694 × 86F3326 and 76L1295 × 91L1492) suggesting additive genetic effects and that recurrent selection will be an effective breeding method.

Availability of Residual and/or Applied Inorganic Phosphorus for Sugarcane Uptake and Growth in a Post-Mined Reconstituted Soil

Mineral sands mining is worldwide an environmental issue and also at the Hillendale mine in KwaZulu-Natal, South Africa. The post-mined soil is to be rehabilitated to sugarcane cropping. One of the concerns with the post-mined soil which is reconstituted with a 70:30 mixture of sand: slimes (silt-plus-clay fraction), is its low phosphorus (P) status, which could be limiting for optimum sugarcane production. A field experiment was conducted on a reconstituted soil at Hillendale to establish the availability of either residual or applied inorganic P to the plant and first ratoon sugarcane crop. Four treatments were evaluated including those where P fertilizer was omitted, applied at half the recommended rate or introduced equal to the recommended rate according to chemical analysis of the soil. In the fourth treatment, no fertilizer was applied at all, whereas nitrogen (N) and potassium (K) were added at recommended rates in the first three treatments. Phosphorus application had a significant effect on sugarcane fractional light interception and aboveground biomass yield of the plant and first ratoon crops, and stalk length and diameter of the first ratoon crop. Pol, brix, purity and fibre content and tiller number were not affected by P application. The application of P increased the foliar N, P, K, calcium (Ca), magnesium (Mg) and sulphur (S) contents of both crops. However, foliar N, P and K were deficient in the first ratoon crop even in the case where fertilizer was applied at the recommended rates, which could have been because of waterlogging. The possible effect of waterlogging on P uptake needs to be addressed in future studies in this reconstituted soil.

Trends in Starch and Sucrose Content among Sweet Sorghum Genotypes and Implications for Sucrose and Ethanol Production

Sweet sorghum has been suggested as a feedstock into the sugarcane mills for sucrose production in Zimbabwe and Swaziland. Sweet sorghum is widely grown by subsistence farmers and matures in 3 to 6 months in February, March and April, before sugarcane harvesting begins. Sweet sorghum has low sucrose content that is difficult to extract during processing. The hypothesis of the study was that sweet sorghum was a potential feedstock to sugarcane mills for the production of sugar and ethanol. The objective of this study was to investigate the trends in starch and sucrose content of four sweet sorghum genotypes namely M337, M81-E, Theis and Topper, and evaluate the potential of sweet sorghum as a feed stock for sugar and ethanol production. The sorghum juice was collected on August 10, August 24, September 8, September 18 and October 2, 2006 and starch and sucrose content were determined. There were significant （P 〈 0.001） genotypes by sampling date interaction effects. Both starch and sucrose content increased with crop sampling date. Genotypes M337 and Theis were late maturing for sucrose content compared to M81-E and Topper. All genotypes except M337 produced no significant increase in starch after 101DAP. Trends in sucrose and starch content were similar, indicating the reason sucrose was difficult to extract from sweet sorghum. The impact of this study would be boosting the incomes of small scale growers who would be subcontracted by the sugar mills to produce sweet sorghum as a feedstock to the mills before sugarcane matures.

Eggs of Ephestia kuehniella and Ceratitis capitata, and motile stages of the astigmatid mites Tyrophagus putrescentiae and Carpoglyphus lactis as factitious foods for Orius spp.

Several factitious foods were assessed for rearing the anthocorid predators Orius thripoborus （Hesse） and Orius naivashae （Poppius） （Hemiptera： Anthocoridae） in the laboratory. Developmental and reproductive traits of both Orius species were examined when offered frozen eggs of the Mediterranean flour moth, Ephestia kuehniella Zeller, frozen processed eggs of the medfly, Ceratitis capitata Wiedemann, or mixed motile stages of the astigmatid mites Tyrophagusputrescentiae （Schrank） or Carpoglyphus lactis （L）. Whereas C. lactis and T. putresecentiae proved to be an inferior food for rearing O. thripoborus and O. naivashae, eggs of C. capitata fully supported development and reproduction of both predators. Results on medfly eggs were similar or slightly inferior to those on E. kuehniella eggs, which is the standard food for culturing these anthocorid bugs. O. thripoborus could be maintained for 4 consecutive generations on C. capitata eggs indicating that processed medfly eggs can be a suitable and cheaper alternative to E. kuehniella eggs for prolonged rearing of these Orius spp.