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Seed Yield, Oil Yield, and Fatty Acid Profiles under Climate Change
Crop yield and quality are influenced by GCC directly through abiotic stresses and indirectly through biotic stresses, especially pathogens that they themselves will change as climate changes, but may increase in virulence (Newton et al., 2011). Seed and oil yield of annual and perennial oilseed crops and oil-bearing plants are interrelated and complex traits that result from multivariate relationships and compensation between many yield components and crop characteristics, as well as interaction with management and environmental factors. Seed yield, stability, and response to external inputs have been and remain key traits in many oilseed-breeding programs. Achieving higher seed yield would considerably reduce environmental impacts associated with seed and oil production of oilseed crops (Li and Mupondwa, 2014). The challenge under GCC stress is to simultaneously optimize seed yield and maintain, if not increase, oil content, oil yield, protein yield, and optimize fatty acid profiles whether for food (PUFAs) or industry (SFAs).
Several factors, including genetic effects of the embryo, cytoplasm, and maternal tissues, as well as genotype × environment × management interactions determine to a large extent the oil content in oilseed crops and oil-bearing plants. Oilseed crops having the C3 metabolic pathway may respond positively to e[CO2] by producing more biomass and accumulating more carbohydrates, thus diluting seed proteins and macro and micronutrients, and may improve oil quality by raising PUFAs at the expense of SFAs (Pal et al., 2014). However, the favorable effect of e[CO2] may be negated by the attendant higher temperatures, lower WUE, and the subsequent accelerated plant development that could result in reduced seed and oil yields. Therefore, key targets in oilseed improvement under GCC stress include increasing overall oil yield and stability on a per seed or per fruit basis and maintaining very high PUFA content for premium edible oil and high SFA contents for oleochemicals used in industrial and pharmaceutical applications (Murphy, 2014).
Oil physical properties (e.g., fluidity) and metabolism are affected by its SFA and PUFA composition. Plant species, genotypes, temperature, environmental conditions, and management practices, in decreasing order, influence FA profiles (Schulte et al., 2013). The large variation in oil content and FA profiles in seed or fruit of wild (e.g., Manihot esculentus and Plukenetia volubilis L), semi-domesticated (e.g., Jatropha curcas), and domesticated oilseed crops and oil-bearing plants (e.g., B. napus and Olea europaea) emphasize the role of genetic diversity within and among species. For example, oil content from Manihot spp. seed range from 17.2% in Manihot caerulescens to 30.7% in Manihot flabellifolia (Alves et al., 2014). Five FAs were found in all Manihot spp. with the average content of linoleic (C18:2) 61.5%, oleic (C18:1) 20.0%, palmitic (C16:0) 12.3%, stearic (C18:0) 4.5%, and linolenic (C18:3) 1.7%. FA contents varied significantly between and within oilseed and oil-bearing plant species. For example, the highest content of linoleic acid (average 65%) was found in seeds of Manihot carthaginensis, M. cecropiaefolia, M. flabellifolia, M. glaziovii, M. peruviana, and M. pseudoglaziovii; and the highest level of oleic acid (average 23%) was found in seed of M. anomala, M. caerulescens, M. dichotoma, M. esculenta, and M. tomentosa. Comparable levels of variation within and among SFA and PUFA content in other oilseed crops may reflect adaptive strategies for seed survival and seedling establishment under contrasting climate conditions. Higher PUFA content may have evolved as an adaptation to cold climates (Wilkes et al., 2013); however, a wide range of these FAs was observed under warmer climates as well. The FA composition of oilseed crops, such as G. max, B. napus, Camelina sativa, and H. annuus, synthesized and accumulated more monounsaturated and less PUFAs when growing temperature was experimentally raised from 10°C to 40°C (Schulte et al., 2013).
Differences among plant species, rather than climate, may explain a large part of the relative abundance of common FAs in oilseed crops, while the role of genetics in regulating plastic response to GCC is well documented. In regional studies (e.g., Zhang et al., 2015), the level of PUFAs increased with latitude and decreased with both mean annual temperature and precipitation; temperature’s impact was more pronounced than that of precipitation. Oil content (27.5–37.2%) and FA composition, mostly PUFAs, varied among Camelina sativa genotypes with year and growing seasons