Résumé
Madagascar heavily depends on rice for caloric intake, especially through irrigated farming. In the Vakinankaratra region, rainfed upland rice farming is an important complement but faces challenges such as poor soil fertility and vulnerability to pathogens like Pyricularia oryzae.
To address these challenges, we evaluated extended elite lines upland rice varietal mixtures adapted to local conditions, focusing on yield performance, stability, and food security.
Four upland rice varieties: Chhomrong Dhan, FOFIFA 172, FOFIFA 173, and FOFIFA 180, well-suited to Madagascar's high-altitude climatic conditions and resistant to Pyricularia oryzae, were evaluated in three experiments conducted in the highlands of Madagascar between 2013 and 2017. The experimental design assessed all variety combinations, considering two treatment factors: 'mixture type' (ranging from pure stands to mixtures of all four varieties) and 'varietal composition' (15 modalities representing different varietal combinations). The analysis included the identification of the best-performing varietal compositions using a mixed-effects linear regression model and land equivalent ratio calculations.
The analysis revealed that grain yield did not significantly differ among various mixture types, while varietal composition within mixtures had a highly significant effect. No mixture combination yielded more than the best varieties in pure stand although some matched their performance. Three combinations showed a significantly improved land equivalent ratio. Varieties differed in competitive abilities and trait plasticity.
Contrary to literature suggesting that increased diversity through varietal mixtures enhances production, the study found that the number of varieties in mixtures (mixture type) did not have significant effects. However, it appears possible to identify specific mixture combinations with strong mixing abilities.
This study evaluated mixtures of elite rice varieties that are currently available to farmers, under optimal fertility management. In these conditions, varietal mixtures did not demonstrate clear advantages over pure stands. However, results may differ under low-fertility conditions more representative of farmers’ fields, or when using a broader genetic diversity. These scenarios warrant further investigation. In such contexts, varietal mixtures could complement other diversification strategies aimed at enhancing the resilience of agricultural systems, particularly in vulnerable regions such as the Madagascar Highlands.
•All mixture combinations of four registered varieties, selected for high-altitude were evaluated.•No mixture outperformed the best varieties in pure stands, but some matched them.•The number of varietal components had no significant effect on mixture yields.•Some varieties showed plasticity in plant height and tillering across mixtures.•On-farm evaluation needed for more mixture combinations under low input conditions.