The efficiency of a breeding programme with progressively advanced targets applied in an elite cultivar of snap bean

Abstract

The objective of this study was to assess the efficiency of a pedigree intra-cultivar selection, based on widely spaced individual plant performance, in a traditional snap bean (Phaseolus vulgaris L.) cultivar, aiming to restore or even improve the cultivar. The programme started with the target of earliness and yield stability, and was progressively advanced with the target of seed shape uniformity. Two parallel pathways were followed: under greenhouse conditions (four generations of selection) and under field conditions (two generations of selection). The average response to selection was 2·43–3·15 and 0·13–0·42 pods/plant per generation for earliness and yield, respectively. The coefficient of variability (CV) of earliness decreased from 81·33 to 39·43 % and from 61·31 to 42·51 % for greenhouse and field grown progenies, respectively. For yield, the CV showed a low decreasing rate, and was stabilized at the end-value of almost 28 %. The results were confirmed during two direct evaluation tests. Firstly, the evaluation of 21 families, as individual spaced plants, showed mean values for earliness of 18·99–22·94 pods/plant and for yield of 32·89–33·09 pods/plant. Secondly, the evaluation of improved selections from the greenhouse and the field and of the source cultivar, in a dense stand, showed that all the selections produced high and stable early fresh pod harvest even 53 days after planting, while the control was still at the vegetative phase. The yield of selected progenies was 219–242 % superior compared with source material. Also, seed stocks of all selections were of the normal long shape. Short-seed progenies were excluded from the breeding programme, since they lacked earliness and stability of performance. The results demonstrate conclusively that it is possible to simultaneously improve earliness and pod yield through diminishing plant-to-plant variability.