Early generation selection strategies for breeding better combinations of cotton yield and fibre quality

This research investigated the use of elite parents and breeding selection strategies for reducing the negative association between cotton yield and fibre quality. Three populations, each with 100 lines developed from high yielding and high fibre quality parents were advanced in a pedigree method to the replicated stage with no selection in any generation. A yarn quality index (YQI) was used as a measure to integrate different fibre properties of length, strength and fineness. Each population had similar means and good genetic variation existed for lint percent (LP) and fibre quality traits in the single plant (SPS) stage; as well as for yield, fibre quality and YQI traits in the Progeny Row (PR) stage and in the following two years of replicated experiments. There were significant associations between SPS (P < 0.05) or PR (P < 0.01) and subsequent replicated data for yield and fibre quality traits. LP at the SPS and yield at PR stage could successfully select highest yielders as measured in subsequent replicated experiments; broad sense heritability was high for all measures. Retrospective analysis determined the proportion required in early generation selections of SPS and PR to successfully identify the highest ranked lines for mean yield and quality in subsequent replicated experiments. Populations had similar proportions (10%) with high yield (>2000 kg lint ha−1) and high quality (YQI > 62), but the populations differed in the numbers of lines with low yield (<1800 kg lint ha−1). For combining high yield and YQI, to capture all 29 lines which subsequently had high yield and YQI in replicated experiments, it would have been necessary to select 55-89% of the highest yielding lines in PR, which would lead to large numbers if lines were to be assessed in replicated experiments. A selection strategy to improve yield and fibre quality combinations which would successfully keep the majority of best lines, would be to select the best 27% of yielders and best 11% of YQI from PR, then select for the best combinations of yield and YQI in replicated experiments. We identified one line which broke the negative relationship between yield and fibre quality within these populations. We conclude that early generation selection for LP, yield and quality would enable unsuitable lines to be discarded so chosen lines could be better assessed in later generations.