The Influence of Environment on Agro-Morpho-Physiological characteristics of pigeon-pea (Cajanus Cajan L.) Genotypes

Abstract

Pigeon pea (Cajanus cajan (L.) Millsp.) is a multipurpose legume grown in tropical and subtropical regions. It serves as a dietary protein source for humans, provides fodder for livestock, and improves soil fertility through nitrogen fixation. It is tolerant to drought and high-temperature stress and grows well in poor soils, making it well-suited to semi-arid regions of South Africa. The crop is cultivated as a backyard species by smallholder, resource-poor farmers in the dry environments of the Limpopo and North West provinces, which are characterised by low rainfall and poor soils. However, pigeon pea remains underutilised due to the lack of candidate cultivars identified and recommended for different agro-ecological zones in South Africa. Furthermore, existing genotypes are unimproved landraces that have not been promoted for large-scale cultivation. This study aimed to evaluate the agro-morpho-physiological characteristics of 25 pigeon pea genotypes across three sites in the Limpopo and North West provinces to identify those best suited to these environments. The twenty-five pigeon pea genotypes were sown during the summer cropping season at Mafikeng (North-West University Experimental Farm), Groblersdal (Loskop Experimental Farm), and Thohoyandou (University of Venda Experimental Farm). Field experiments were arranged in a randomised complete block design (RCBD) with three replications. Seeds were sown manually at an intra-row spacing of 0.5 m and an inter-row spacing of 1.0 m. Soil samples were collected at depths of 0–30 cm and 30–60 cm before planting. Crop phenology (days to 50% emergence and 50% flowering) and growth parameters (plant height, stem diameter, leaf length, leaf width, and number of branches) were determined at 50% flowering. Chlorophyll and anthocyanin content were measured at this stage using a chlorophyll meter (CCM-200 PLUS, Opti-Sciences, Tyngsboro, MA, USA) and an anthocyanin meter (ACM-200 PLUS, Opti-Sciences, USA), respectively. Grain yield and yield components (pod weight per plant, number of pods per plant, pod length, pod width, and 100-seed weight) were determined at maturity. Data were subjected to two-way analysis of variance (ANOVA) using GenStat (23rd edition; VSN International, 2023), and mean separation was performed using Tukey’s Honestly Significant Difference (HSD) test at the 5% probability level. Additive main effects and multiplicative interaction (AMMI) and genotype plus genotype-by-environment (GGE) analyses were used to assess performance, stability, and adaptation across environments. The environment effect was significant for days to 50% flowering, while the genotype effect was significant for both days to 50% emergence and flowering. The genotype × environment interaction (GEI) was not significant for emergence but was significant for flowering. For plant height, stem diameter, and leaf length, environment and GEI effects were not significant, whereas genotype effects were significant. The effects of environment, genotype, and GEI were significant for the number of branches. Similarly, genotype and GEI effects were significant for chlorophyll and anthocyanin content. Grain yield was significantly influenced by environment, genotype, and GEI, with Loskop recording the highest mean yield (678.4 kg ha⁻¹). Yield ranged from 242.5 kg ha⁻¹ (GC-P018) to 678.4 kg ha⁻¹ (GC-P003). The significant GEI indicates that genotypes responded differently across the three sites. AMMI analysis also showed significant genotype, environment, and interaction effects on yield, with IPCA1 and IPCA2 accounting for 85.4% and 14.6% of the variation, respectively. Genotypes with IPCA1 values close to zero were considered more stable. Genotypes GC-P003, GC-P024, GC-P022, GC-P011, GC-P014, and GC-P025 were identified as high yielding, whereas GC-P018 and GC-P007 were low yielding. Based on AMMI stability values (ASV), GC-P020 was the most stable genotype across all sites, with the lowest ASV (3.60). The GGE biplot grouped Mafikeng (E1) and Loskop (E2), while Thohoyandou (E3) formed a separate cluster. The “which-won-where” pattern showed that GC-P003 and GC-P024 performed best in Loskop, whereas GC-P016 and GC-P009 performed best in Thohoyandou. No genotype was specifically adapted to Mafikeng. GC-P024 was identified as the ideal genotype, located near the centre of the biplot. Genotypes GC-P003, GC-P022, GC-P024, GC-P011, GC-P014, and GC-P025 are recommended for inclusion in breeding programmes for further evaluation due to their high yield performance across environments. However, further testing across additional locations and seasons is recommended before cultivar release. Breeding programmes should consider both yield performance and stability indices when selecting pigeon pea genotypes for cultivation.