Relating cultivar Pachymetra root rot resistance to sugarcane yield using breeding selection trial analyses

Plant breeders conduct a range of yield trials each year to estimate the yielding potential of sugarcane clones progressing through the breeding program. Only the highest-yielding clones are selected for further testing with very small numbers being released as commercial cultivars. Disease susceptibility varies greatly amongst the tested clones and a number of diseases influence the yield of clones in various stages of the selection process. Disease resistance testing is an important routine aspect of the breeding program. All clones for northern Queensland are screened for disease resistance, while selected clones from other areas are tested for resistance to Pachymetra root rot. Two new terms are introduced: resistance index (RI) and the yield loss resistance index (YLRI). Analyses were conducted relating yielding ability of clones in stage 3 trials to Pachymetra resistance. Pachymetra root rot on average reduced tonnes cane per hectare by 15.8% and tonnes sugar per hectare by 10.2%. There was a slight positive effect on commercial cane sugar. YLRI5 for tonnes cane was 3.5 and for tonnes sugar 5.7. With a RI of 3.7, the current breeding strategy for northern Queensland appears appropriate. The data reported here will be valuable for refining selection strategies to improve breeding efficiencies. These analyses could be undertaken each year using data from all breeding trials throughout Queensland, not only with Pachymetra root rot, but also with other diseases normally endemic in cane fields. The advantage of this technique is that with a minimum of further expenditure, ongoing estimates of disease-induced yield losses can be obtained with the information guiding the selection program.