Morphological diversity in a barley Composite Cross derived Population evolved under low-input conditions and its relationship with molecular diversity: indications for breeding

In order to reduce the environmental impacts of agriculture and improve the resilience and the sustainability of our food systems, there is an increasing interest in shifting from the present agricultural systems, which are characterized by a high content of external input, to low-input productive systems characterized by high resilience and sustainability. Purposely developed varieties are needed for the latter. With the rapid disappearance of landraces, heterogeneous populations like Composite Cross Populations (CCP) or line mixtures, developed through evolutionary plant breeding, can be the ideal source of breeding materials for the development of new cultivars for low-input productive systems. Parental lines of CCPs should be selected among old breeding lines, varieties or landraces because the specific characteristics required for low-input or organic farming systems might have been lost during selection of modern varieties. In the current scenario of renewed interest for evolutionary plant breeding, the evolution of diversity in heterogeneous populations needs to be better investigated to maximize the advantages that can be obtained by their utilization. In this paper we report the analysis of 88 barley plants, randomly chosen from a CCP, namely AUT DBA (where AUT indicates autumnal sowing and DBA is the acronym of the former Department), multiplied for 13 years under a low-input management system without any conscious human selection aiming at (i) investigating the morphological diversity still existing in the population and its potential value as source of breeding materials for low-input/organic agriculture and (ii) understanding the traits that contributed to the adaptive success of certain groups of individuals. Eighteen plant and spike morphological traits were analysed using bi-dimensional spatial analysis, cluster analysis, non-parametric tests and multivariate approaches. Low lodging and loose smut damage were observed in the CCP where several individuals were superior to the best control for at least one of the four yield-related traits, namely spike weight (sw), number of seeds per spike (nss), weight of seeds in a spike (sws) and kernel weight (kw). Three morphological clusters were identify using cluster analysis. Clusters 2 and 3 grouped the largest part of CCP individuals which, compared with those in cluster 1, were mainly characterized by heavier spikes with higher seed number, taller culms and early flowering. Interestingly, the plant architecture of all the controls was different from that of the most frequent genotypes in the CCP, showing that low-input systems may require a plant architecture different from the one usually considered as the most suitable for high input systems. Taking advantage of results from Raggi et al. (2015), phenotypic data were also analyzed according to individual genetic group assignment. Results suggest that plant height at the beginning of stem elongation (ph1), and days to heading (dth), together with traits related to culm and leaf morphology, could have played a significant role in determining the success of plants from genetic group D which is the most represented in the CCP. According to the wide range of morphological diversity existing in the AUT DBA and the high percentage of lines that show favorable combinations of different traits, this population can be a useful gene-pool for selecting lines for breeding activities. Even if further use of the CCP for breeding purposes could be limited by its possible evolution, there are different ways of manipulating the CCP to counteract the undesirable changes without great economic and/or technical efforts. The high number of multilocus genotypes and the evolutionary responses observed in AUT DBA show that the prediction that phenotypic microevolution in natural systems may be limited by low genetic variances in harsh environments and low selection pressure in good environments is not necessarily true for low-input systems.