Pea Breeding for Intercropping With Cereals: Variation for Competitive Ability and Associated Traits, and Assessment of Phenotypic and Genomic Selection Strategies

Abstract

Mixed stand (MS) cropping of pea with small-grain cereals can produce more productive and environment-friendly grain crops relative to pure stand (PS) crops but may require selection to alleviate the pea competitive disadvantage. This study aimed to assess the pea variation for competitive ability and its associated traits and the efficiency of four phenotypic or genomic selection strategies. A set of 138 semi-leafless, semi-dwarf pea lines belonging to six recombinant inbred line populations and six parent lines were genotyped using genotyping-by-sequencing and grown in PS and in MS simultaneously with one barley and one bread wheat cultivar in two autumn-sown trials in Northern Italy. Cereal companions were selected in a preliminary study that highlighted the paucity of cultivars with sufficient earliness for association. Pea was severely outcompeted in both years albeit with variation for pea proportion ranging from nearly complete suppression (<3%) to values approaching a balanced mixture. Greater pea proportion in MS was associated with greater total yield of the mixture (r ≥ 0.46). The genetic correlation for pea yield across MS and PS conditions slightly exceeded 0.40 in both years. Later onset of flowering and taller plant height at flowering onset displayed a definite correlation with pea yield in MS (r ≥ 0.46) but not in PS, whereas tolerance to ascochyta blight exhibited the opposite pattern. Comparisons of phenotypic selection strategies within or across populations based on predicted or actual yield gains for independent years indicated an efficiency of 52–64% for indirect selection based on pea yield in PS relative to pea yield selection in MS. The efficiency of an indirect selection index including onset of flowering, plant height, and grain yield in PS was comparable to that of pea yield selection in MS. A genome-wide association study based on 5,909 SNP markers revealed the substantial diversity of genomic areas associated with pea yield in MS and PS. Genomic selection for pea yield in MS displayed an efficiency close to that of phenotypic selection for pea yield in MS, and nearly two-fold greater efficiency when also taking into account its shorter selection cycle and smaller evaluation cost.

Supply Chain Perspectives on Breeding for Legume–Cereal Intercrops

“…Application of Function-Structural Plant Models (FSPM) and process-based minimalistic models could significantly reduce the complexity of intercrop breeding, and minimize the need for experimental evaluation of multiple crop genotype combinations and spatial designs ( Berghuijs et al, 2020 ; Blanc et al, 2021 ; Bourke et al, 2021 ). While simulation has shown the utility of genomic selection for intercrop breeding ( Bančič et al, 2021 ), using both phenotypic and genomic selection tools is strongly recommended ( Annicchiarico et al, 2021 ; Wolfe et al, 2021 ). Additionally, methods for estimating both general and specific mixing ability correlated with simple-to-measure indicator traits could provide a cost-efficient and effective methodological framework for intercrop breeding ( Haug et al, 2021 ).…”

“…For example, selection for yield in an intercrop should aim to maximize complementary resource use and minimize asymmetrical competition, as the overall yield of intercrops often depends on the yield of the less-competitive component ( Harper, 1977 ; Kammoun et al, 2021 ). This stresses the importance of selecting for competitive ability of less-competitive crop partners ( Annicchiarico et al, 2021 ), particularly when the less-competitive species is also more economically valuable, which is often the case for legumes ( Hamann et al, 2020 ).…”

Legume Breeding for the Agroecological Transition of Global Agri-Food Systems: A European Perspective

“…Breeding for intercropping may be challenging for legume breeders, requiring the identification of trait mean and variance that are responsible for the survival and the production of a target species grown with one or several companion species (Maamouri et al, 2017). Specific breeding for intercropping is supported by several studies on perennial legumes reviewed in Annicchiarico et al (2019a), as well as by recent findings for an annual legume, such as pea (Annicchiarico et al, 2021).…”

“…Pioneer studies highlighted greater predicted yield gain per unit time or unit cost for alfalfa ( Annicchiarico et al, 2015b ), soybean ( Matei et al, 2018 ), and pea ( Annicchiarico et al, 2019b ). In legumes, GS displayed convenient predictive ability also for key grain quality ( Stewart-Brown et al, 2019 ) or forage quality traits ( Biazzi et al, 2017 ; Pégard et al, 2021 ) and emerging complex traits, such as drought tolerance ( Li et al, 2019 ; Annicchiarico et al, 2020 ), performance in intercropping ( Annicchiarico et al, 2021 ), and tolerance to some biotic stresses ( Carpenter et al, 2018 ). However, research work is crucially needed to fully assess the potential of GS for different legume species and target traits, explore the transferability of its models to different breeding populations, and optimize its adoption within the breeding schemes.…”

Pisum sativum Response to Nitrate as Affected by Rhizobium leguminosarum-Derived Signals

“…Nowadays, including legume-based intercrops in crop successions is gaining renewed interest, as it is considered to be a promising way to ensure a double benefit, namely, decreasing the usage of both N fertilizer and herbicides on top of maintaining good levels of production [ 3 ]. Intercropping, with legumes used as service plants, can help control weeds by competing for soil water, mineral nutrients, and light [ 4 ]. However, legumes are known to be poor competitors for the soil mineral N, and more efficient genotypes would be needed to improve weed control in innovative sustainable cropping systems.…”