Safflower Growth, Development, Yield and Oil Content as Influenced By Genotype and Environment Interaction Under Onfarm Conditions

Abstract

Safflower (Carthamus tinctorius L.) is amongst the neglected and underutilized oilseed crop that is adaptable to environmental conditions present in arid and semi-arid lands (ASALs). It has many uses like foods, textile, pharmaceutical, cosmetic, and industrial (paint, biodiesel). Safflower seed produce healthy and high-quality vegetable oil which is rich in vital linoleic and oleic fatty acids. The economic potential of this crop is very high and has been noticed in Botswana. Recently, the Botswana government has developed a new policy known as Temo-Letlotlo Programme in which the government subsidises inputs for farmers in growing 13 food crops of which safflower is one of them. The goal of this programme is to promote food security, commercialization, inclusivity in agricultural production, and social capital. Therefore, to increase the productivity of safflower in ASALs such as Botswana, genotypes that show greater adaptability and stability for growth, yield, and oil content need to be assessed and recommended to farmers, hence, the aim of this study. In the first study, an on-farm trial was conducted to assess the influence of season, location, and genotype and their interactions on the growth, phenological development, oil content, yield, and yield components of safflower. This study was conducted in summer and winter at three sites (Sebele, Ramonaka, and Molepolole) in the southern part of Botswana using five safflower genotypes (Turkey, Sina, PI537636, Kenya9819, and Gila). The findings demonstrated that winter planting delayed the phenological development (days to emergence (2.56 days), stem elongation (33.3 days), branching (47.8 days), flowering (50 days), and maturity (79.4 days)), and promoted the vegetative growth, yield, yield components, and oil content of safflower (plant height (38.7%), shoot biomass (218%), root biomass (239%), capitula number/plant (18.6%), capitula diameter (4.7%), capitula weight (30%), 1000-seed weight (17.8%), seed yield/ha (84.4%), oil content xviii (20.7%) and oil yield (114.2%)). Safflower planted in winter at Ramonaka had better vegetative growth (plant height (90.6 cm), root biomass (13.2 g/plant), and shoot biomass (132 g/plant)) than that of other locations planted either in winter or summer. The results further revealed variability amongst the studied genotypes for almost all the phenological development (days to emergence, stem elongation, branching, flowering, and maturity), growth (plant height and shoot biomass), oil content seed yield, and yield components traits studied (capitula number/plant, capitula diameter, capitula weight, and 1000-seed weight). In addition, location, season, and their interactions significantly affected these parameters (number of primary branches/plant, capitula/plant, capitula weight, 1000-seed weight, seed yield, oil content, and oil yield/ha). Genotype by environment interactions (GGE) biplots for seed yield demonstrated that Sebele showed greater representativeness and discriminative ability therefore, it was considered a perfect site for choosing genotypes that are adapted to the entire region. Genotype Kenya9819 was identified as the highest seed-yielding and stable genotype based on the GGE biplots. When evaluating genotypes based on overall superiority, the genotype by yield*trait combination (GYT) biplot showed that genotypes Turkey and Kenya9819 had an above-average seed yield-trait combination, hence superior, while genotypes Gila and PI537636 performed poorly (they were below-average for all studied traits except for yield*oil content). Therefore, genotypes Turkey and Kenya9819 were recommended to be grown in the southern part of Botswana based on their overall superiority. On the other hand, genotype Gila could be used for breeding purposes to improve the seed oil content of other genotypes due to its high seed oil content. The second study determined the relationship between oleosin genes and oil bodies in regulating the oil content of safflower seeds. This was achieved by isolation and quantifying the oleosin genes and oil bodies from the seeds of five (Gila, Turkey, Sina, PI537636, and Kenya9819) safflower genotypes using qPCR and fluorescence xix microscope, respectively and assessed them against the seed oil content. The results revealed a strong inverse relationship where smaller oil bodies were exhibited by genotypes containing high oil content (Kenya9819 and Gila) and high relative expression of oleosin genes. The findings indicated that oleosin genes and oil bodies are important traits to consider when characterizing oil seed crops for oil content. In the third study, the response of safflower genotypes to drought stress was evaluated under a greenhouse and verified under field conditions. Drought stress was found to reduce the chlorophyll content, leaf relative water content (LRWC), and plant height irrespective of stage of development, genotype, and stress duration. For instance, at days 20 and 30, drought stress reduced chlorophyll content by 37.8% and 63.7%, respectively, during the branching stage under the greenhouse. Furthermore, the levels of ascorbate peroxidase (APX) and proline escalated in response to drought stress irrespective of genotype, developmental stage and stress duration. For example, drought stress increased the APX content by 1.03 and 15.6X higher in stressed plants after 10 and 20 days of drought stress, respectively than control plants during the flowering stage in the greenhouse. This trend was observed in both the greenhouse and field experiments. There was a substantial (P.....