How does the harvest index affect water‐use efficiency and nutrient‐utilization efficiency of sunflowers (Helianthus annuus L.)?

Abstract

Besides oilseed rape and soybean, sunflower is one of the most important annual oilcrops. Apart from seed yield, which is the most important trait in many crops, oil yield is of utmost interest for sunflower breeders and farmers. Compared to the seed yield of sunflowers, their total biomass is often very high, and it is of great agronomic interest to increase the ratio of both parameters, which is defined as harvest index. With an increase in harvest index, improvements of resource‐use efficiencies can be expected. To generate an adequate seed yield, water and nutrients are key factors and their efficient use becomes increasingly important under conditions of aridity and higher production goals. A pot experiment was conducted in summer 2017 to determine differences in harvest index of various sunflower genotypes which could have an influence on the use efficiencies of water and nutrients (N, P, K). In total, 25 genotypes of different origin and with various morphological traits were investigated under optimal growth conditions. The harvest index varied from 29% to 47% and showed significant differences among some genotypes. The harvest index was less affected by the total biomass of the plants but more by the seed yield. The seed yield itself was mainly determined by the single seed weight rather than by the number of seeds. The experiment also confirmed significant positive correlations between harvest indices and all use efficiencies. Genotypes with high harvest indices were characterized by high oil concentrations in the seeds and particularly by high oil yields. In conclusion, cultivation of sunflower genotypes with high harvest indices most likely results in high water‐use efficiency and high nutrient‐utilization efficiencies as well as in high oil yields.

Drought stress in sunflower causes inhibition of seed filling due to reduced cell‐extension growth

“…The sink size was mainly reduced due to a lower single seed weight under stress (Figure 1c). The higher single seed weight of RGT Llincoln, which was also found by Keipp et al (2019) at maturity, was already observed in the early seed‐filling phase (Figure 1c). These results indicate that RGT Llincoln had a better ability of seed filling than Sy Vivacio already from start of the filling phase.…”

“…The harvest index is the seed yield relative to the total above‐ground biomass and describes the portion of assimilates that is allocated to the seeds as the harvested product (Hütsch & Schubert, 2017; Wnuk et al, 2014). According to Keipp et al (2019), the harvest index of sunflowers is influenced by both, straw yield and single seed weight. RGT Llincoln had a significantly higher harvest index than Sy Vivacio, caused by a higher total biomass and a lower seed yield of Sy Vivacio.…”

“…The third point is equivalent to an improved harvest index which is defined as seed yield per total above‐ground biomass (Hütsch & Schubert, 2017; Wnuk, Górny, Bocianowski, & Kozak, 2014). In an experiment with various sunflower genotypes, we found a positive correlation between harvest index and water‐use efficiency (Keipp, Hütsch, & Schubert, 2019). The results in this study showed that the harvest index of sunflowers was influenced by both, straw yield and single seed weight.…”

“…The present study was designed based on the results of Keipp et al (2019). From the genotype‐screening experiment, two modern sunflower cultivars, one with a high (RGT Llincoln) and one with a low harvest index (Sy Vivacio), were selected for further investigations.…”

New challenges for sunflower ideotyping in changing environments and more ecological cropping systems

“…ANR, PE or AE were not identified as priorities for breeding in sunflower. However, Montemurro and De Giorgio (2005) observed differences in NUE for 2 cultivars at field level and recently Keipp et al (2019) in a pot experiment obtained significant differences for the three nutrient-utilization efficiencies (NUE, PUE, and KUE) among 25 sunflower hybrids.…”