Phenolic profile of grapevine cv. Tempranillo skins is affected by timing and severity of early defoliation

Aim of study: To investigate the effects of three early leaf removal treatments on the phenolic compounds of cv. ‘Tempranillo’ (Vitis vinifera L.) grape skins. Area of study: The experiment was conducted in a vineyard located in Requena, Valencia (South-eastern Spain) over two consecutive seasons. Materials and methods: Four treatments were investigated over two seasons in drip-irrigated vines: Control (C), non-defoliated and three defoliation treatment, applied at different phenological stages and intensities where all leaves from the first 6 nodes were eliminated just before flowering (ED) and at fruitset (LD). The fourth defoliation treatment was performed at the same time of ED but only the leaves facing east of the eight first nodes were removed (EED). At harvest, thirty-eight phenolic compounds were quantified by HPLC in the grape skins, including anthocyanins, flavanols, flavonols, hydroxycinnamic acids and their tartaric derivatives. Main results: A general increase of the skin phenolic compounds concentration was found in response to the defoliation treatments. The largest and more significant effects were observed for LD in 2009 with relative increases with respect to the un-defoliated vines of 14.8, 86.0, 119.0, and 75.9% for anthocyanins, flavanols, flavonols and hydroxycinnamates, respectively. On the other hand, EED did not clearly modify any polyphenolic compound. In addition, the response of phenolic families analyzed to defoliation treatments was different. Malvidine derivatives were not altered by any of the treatments, while the contents of quercetin and kaempferol derivatives and ferulic and coumaric acids, increased in both years when LD was applied. Research highlights: The defoliation effects on specific phenolic substances were dependent on timing, severity, and the season. Skin phenolic compounds increase in response to defoliation treatments and flavonols and hydroxycinnamates were the most affected families.

Shoot–Root Interplay Mediates Defoliation-Induced Plant Legacy Effect

Shoot defoliation by grazers or mowing can affect root traits of grassland species, which may subsequently affect its aboveground traits and ecosystem functioning (e.g., aboveground primary production). However, experimental evidence for such reciprocal feedback between shoots and roots is limited. We grew the perennial grass Leymus chinensis–common across the eastern Eurasian steppe–as model species in a controlled-hydroponics experiment, and then removed half of its shoots, half of its roots, or a combination of both. We measured a range of plant aboveground and belowground traits (e.g., phenotypic characteristics, photosynthetic traits, root architecture) in response to the shoot and/or root removal treatments. We found the regenerated biomass was less than the lost biomass under both shoot defoliation and root severance, generating a under-compensatory growth. Root biomass was reduced by 60.11% in the defoliation treatment, while root severance indirectly reduced shoot biomass by 40.49%, indicating a feedback loop between shoot and root growth. This defoliation-induced shoot–root feedback was mediated by the disproportionate response and allometry of plant traits. Further, the effect of shoot defoliation and root severance on trait plasticity of L. chinensis was sub-additive. That is, the combined effects of the two treatments were less than the sum of their independent effects, resulting in a buffering effect on the existing negative influences on plant persistence by increased photosynthesis. Our results highlight the key role of trait plasticity in driving shoot–root reciprocal feedbacks and growth persistence in grassland plants, especially perennial species. This knowledge adds to earlier findings of legacy effects and can be used to determine the resilience of grasslands.

Direct and Joint Effects of Genotype, Defoliation and Crop Density on the Yield of Three Inbred Maize Lines

The aim of this study was to observe direct and joint effects of three factors (genotypes, ecological environmental conditions and the applied crop density) on the level of defoliation intensity and yield. Three inbred lines (G) of maize (G1–L217RfC, G2–L335/99 and G3–L76B004) were used in the study. The trials were performed in two years (Y) (Y1 = 2016 and Y2 = 2017) and in two locations (L) (L1 and L2) under four ecological conditions of the year–location interaction (E1–E4) and in two densities (D1 and D2) (50,000 and 65,000 plants ha−1). Prior to tasselling, the following five treatments of detasseling and defoliation (T) were applied: T1—control, no leaf removal only detasseling, T2–T5—removal of tassels and top leaves (from one to four top leaves). The defoliation treatments had the most pronounced effect on the yield reduction in G1 (T1–Tn+1… T5), p < 0.05. The ecological conditions on yield variability were expressed under poor weather conditions (E3 and E4), while lower densities were less favorable for the application of defoliation treatments. The result of joint effects of factors was the lowest grain yield (896 kg/ha) in G3 in the variant E3D1 for T2 and the highest grain yield (11,389 kg/ha) in G3 in the variant E2D2 for T1. The smallest effect of the defoliation treatment was on the kernel row number (KRN).

Effects of cotton genotype, defoliation timing and season on fiber cross-sectional properties and yarn performance

Cotton fiber cross-sectional properties influence the performance of ring spun yarns. The spinning performance of two Gossypium hirsutum L. Upland cotton genotypes known to have inherently different fiber fineness properties were compared. Genotypes were grown together in field experiments conducted over two growing seasons, and crops were subjected to early and late defoliation treatments. The aim was to quantify the differences in yarn properties following changes targeting fiber fineness properties in isolation from other fiber properties. For the first time, the percentage difference in yarn properties was captured along with the associated changes made to alternative fiber fineness properties within the base micronaire 3.50 to 4.90 G5 range. As expected the genotype with lower fiber micronaire, linear density, and perimeter, spun yarns that were stronger and more even. Late defoliated cotton plants produced fibers that were higher in micronaire and maturity ratio, and were bigger in perimeter, which demonstrated that the fibers had expanded during the secondary wall thickening phase of development. However, the defoliation treatment effect on fiber fineness properties was smaller compared with the effect of genotype, and no change to any yarn property was detected. In terms of environmental effects, the first season cotton had smaller perimeter finer fibers that spun stronger and more even yarns. In contrast, the second season cotton had bigger perimeter fibers that spun weaker and less even yarns.

Contribution of green organs to grain weight in dryland wheat from the 1940s to the 2010s in Shaanxi Province, China

Eight dryland winter wheat cultivars (Triticum aestivum L.), which were widely cultivated from the 1940s to the 2010s in Shaanxi Province, China, were selected and grown in plots, and two water treatments (irrigation and drought) were used to identify the contribution of ears, leaves and stems to grain weight and grain number associated with cultivar replacement. The plant height and stem dry weight of the dryland wheat decreased significantly during the cultivar replacement process, but there was a remarkable increase in the dry matter translocation of stems under irrigation. Shaded-ear and defoliation treatment could decrease the grain number and grain weight, and the grain weight was more influenced. Both the leaf and ear are important photosynthetic sources for dryland wheat, and the contribution of ear assimilates showed a significant increase over time; however, the contribution of leaf assimilates showed a negative correlation with cultivation over time. The accumulation of stem assimilates and ear photosynthesis both increased the grain weight potential. In the future breeding process, cultivars with more assimilates stored in the stem and greater assimilative capacity of ears, especially a greater contribution of ear assimilates, are expected to increase the grain yield.

Resource manipulation through experimental defoliation has legacy effects on allocation to reproductive and vegetative organs in Quercus ilex

Background and Aims In plants, high costs of reproduction during some years can induce trade-offs in resource allocation with other functions such as growth, survival and resistance against herbivores or extreme abiotic conditions, but also with subsequent reproduction. Such trade-offs might also occur following resource shortage at particular moments of the reproductive cycle. Because plants are modular organisms, strategies for resource allocation to reproduction can also vary among hierarchical levels. Using a defoliation experiment, our aim was to test how allocation to reproduction was impacted by resource limitation. Methods We applied three levels of defoliation (control, moderate and intense) to branches of eight Quercus ilex trees shortly after fruit initiation and measured the effects of resource limitation induced by leaf removal on fruit development (survival, growth and germination potential) and on the production of vegetative and reproductive organs the year following defoliation. Key Results We found that defoliation had little impact on fruit development. Fruit survival was not affected by the intense defoliation treatment, but was reduced by moderate defoliation, and this result could not be explained by an upregulation of photosynthesis. Mature fruit mass was not affected by defoliation, nor was seed germination success. However, in the following spring defoliated branches produced fewer shoots and compensated for leaf loss by overproducing leaves at the expense of flowers. Therefore, resource shortage decreased resource allocation to reproduction the following season but did not affect sex ratio. Conclusions Our results support the idea of a regulation of resource allocation to reproduction beyond the shoot scale. Defoliation had larger legacy effects than immediate effects.

Partial defoliation of Brachypodium distachyon plants grown in petri dishes under low light increases P and other nutrient levels concomitantly with transcriptional changes in the roots

Background There have been few studies on the partial defoliation response of grass. It has been unclear how partial defoliation may affect roots at the levels of nutrient accumulation and transcriptional regulation. Hereby we report a comprehensive investigation on molecular impacts of partial defoliation by using a model grass species, Brachypodium distachyon. Results Our Inductively Coupled Plasma Mass Spectrometry analyses of B. distachyon revealed shoot- and root-specific accumulation patterns of a group of macronutrients including potassium (K), Phosphorus (P), Calcium (Ca), Magnesium (Mg), and micronutrients including Sodium (Na), iron (Fe), and Manganese (Mn). Meanwhile, our genome-wide profiling of gene expression patterns depicts transcriptional impacts on B. distachyon roots by cutting the aerial portion. The RNAseq analyses identified a total of 1,268 differentially expressed genes in B. distachyon with partial defoliation treatment. Our comprehensive analyses by means of multiple approaches, including Gene Ontology, InterPro and Pfam protein classification, KEGG pathways, and Plant TFDB, jointly highlight the involvement of hormone-mediated wounding response, primary and secondary metabolites, and ion homeostasis, in B. distachyon after the partial defoliation treatment. In addition, evidence is provided that roots respond to partial defoliation by modifying nutrient uptake and rhizosphere acidification rate, indicating that an alteration of the root/soil interaction occurs in response to this practice. Conclusions This study reveals how partial defoliation alters ion accumulation levels in shoots and roots, as well as partial defoliation-induced transcriptional reprogramming on a whole-genome scale, thereby providing insight into the molecular mechanisms underlying the recovery process of grass after partial defoliation.

Carbon partitioning between shoot organs following early leaf removal

In grapevines, basal leaf removal at bloom often induces a reduction of fruit set. The effect is related to a reduction in carbon availability for different plant organs competing for photosynthates. To understand and quantify carbon allocation among major sink organs following the early basal leaf removal, the effect of early basal defoliation was studied in Pinot noir grapevines. The experiment was performed in Michigan, a cool climate viticultural region, and three levels of defoliation were imposed at full bloom: (1) no leaves removed (DF-0); (2) six leaves removed from six basal nodes (DF-6); and (3) ten leaves removed from ten basal nodes (DF-10). A week after the defoliation treatment, 13C pulsing was executed to the defoliated shoots. Photosynthesis (Pn), carbon distribution, fruit set, vine performance and basic fruit composition were measured. LR treatments induced higher Pn when compared to LR-0. The highest 13C allocation (%) was recorded in the shoot apex of the LR-10 treatment and LR-10 had the lowest percentage of 13C transported to the cluster, with a reduced fruit set of about 60% when compared to LR-0. The severity of leaf removal reduced significantly fruit set and increased shoot apex sink strength at the expense of the cluster.

Tolerance of Swallowworts (Vincetoxicum spp.) to Multiple Years of Artificial Defoliation and Clipping

The European vines pale swallowwort and black swallowwort are invading various habitats in northeastern North America. It is unclear how these plants might respond to potential biological control agents, as they experience little herbivore damage in North America, or longer durations of mowing given the reported lack of efficacy of mechanical control. We evaluated the effect of six seasons of artificial defoliation (50 or 100% defoliation once or twice per season) and clipping (once, twice, or four times at 8 cm above the soil level) on the survival, growth, and reproduction of mature plants of the two species grown in a common garden field experiment. No plants died from damage after 6 yr. Black swallowwort produced more aboveground biomass, whereas pale swallowwort produced more root biomass and root crown buds, compared with its congener species. For most damage treatments, root biomass and the number of crown buds and stems increased over time, whereas aboveground biomass and viable seeds per plant generally did not change. Substantial overlap in plant size and seed production occurred among damage treatments and species. The most severe defoliation treatment did not substantially limit growth and reproduction compared with undamaged plants. While two clippings per season sometimes prevented seed production, four clippings per season was the only type of damage that consistently prevented plant growth and eliminated seed production. Pale and black swallowwort display a high tolerance to aboveground tissue loss in high-light environments without plant competition. The annual increase in plant size calls into question the potential efficacy of a defoliating insect against field populations of swallowworts, and it seems likely the only benefits of a long-term mowing regime will be to eliminate seed production.