Intense selection by pesticides and antibiotics has resulted in a global epidemic of evolved resistance. In agriculture and medicine, using mixtures of compounds from different classes is widely accepted as optimal resistance management. However, this strategy may promote the evolution of more generalist resistance mechanisms. Here we test this hypothesis at a national scale in an economically important agricultural weed: blackgrass (Alopecurus myosuroides), for which herbicide resistance is a major economic issue. Our results reveal that greater use of herbicide mixtures is associated with lower levels of specialist resistance mechanisms, but higher levels of a generalist mechanism implicated in enhanced metabolism of herbicides with diverse modes of action. Our results indicate a potential evolutionary trade-off in resistance management, whereby attempts to reduce selection for specialist resistance traits may promote the evolution of generalist resistance. We contend that where specialist and generalist resistance mechanisms co-occur, similar trade-offs will be evident, calling into question the ubiquity of resistance management based on mixtures and combination therapies.

Four diverse alfalfa (Medicago spp.) populations were screened in the field for nutritional quality. Acid detergent fiber of composite samples from first and second harvests was used to select for dry matter digestibility. First‐harvest percent transmittance, a Udy dyebinding procedure, was used to estimate crude protein concentration. Comparisons with standard cultivars showed that one cycle of selection was effective in reducing total cell wall, lignin, and amount of cell wall lignification and in increasing crude protein, hemicellulose (when expressed as a fraction of cell wall), in vitro dry matter digestibility, and in vitro cell wall digestibility in three of the four populations. Improved digestibility was associated with an increase in hemicellulose and a decrease in lignin fractions of the cell wall. Cellulose (when expressed as a fraction of the cell wall) did not change with selection. The mean crude protein concentration of the most improved population was 208 g kg−1, and total digestible dry matter was 775 g kg−1 as compared to 199 and 756 g kg−1, respectively, measured for the mean of standard cultivars. These differences correspond to an increased crude protein yield of approximately 200 kg ha−1 yr−1 and an increased digestible dry matter yield of approximately 525 kg ha−1 yr−1.

The output can be accessed at: https://repository.rothamsted.ac.uk/item/98769/theblackgrass-genome-reveals-patterns-of-non-parallel-evolution-of-polygenic-herbicideresistance.

A diverse alfalfa population derived from crosses within and among the species Medicago sativa L., M. falcata L., and M. caerulea Less. was evaluated for variation in acid‐detergent fiber (ADF) and crude protein (CP) concentration. A sequential selection scheme based on first and second harvest ADF, CP, and yield was developed to identify vigorous plants with differing levels of the nutritional characteristics. An analysis of two five‐parent diallel sets indicated that variation in ADF and CP concentration among crosses was accounted for primarily by general combining ability. Four experimental synthetics were grown in small plots and evaluated for yield and nutritional quality. The low fiber and high protein synthetics averaged 5.7% (1.9 units) lower in ADF, and 7.2% (1.5 units) higher in CP than the cultivars Vernal and Honeoye

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Sequential selection for agronomic vigor, high crude protein (CP) concentration, and low acid detergent fiber (ADF) concentration has been proven to increase forage quality of alfalfa (Medicago spp.) when subjected to the harvest schedule (three harvests at 6‐wk intervals, beginning late May) recommended for most of New York. No research has been reported to indicate that forage quality and yield of alfalfa populations bred for improved forage quality are also improved under other harvest systems. The objective of this research was to compare three forage quality‐improved alfalfa synthetics to ‘Saranac AR’ and ‘Oneida VR’ for nutritive value and forage yield under three harvest‐management systems typically used in the northeastern USA. Field experiments were conducted at two locations for two production years. Soil types were Rhinebeck silt loam (fine, illitic, mesic Aeric Ochraqualt) and Williamson silt loam (coarse‐silty, mixed, mesic Typic Fragiochrept). The management systems, each based on three harvests per year, varied in date of initial harvest (recommended first harvest date vs. a 10‐d delay) and in regrowth interval (5 vs. 6 wk between Harvests 1 and 2). The quality‐improved synthetics averaged 2 and 6% lower forage yield in 1985 and 1986, respectively. The synthetics developed partly from exotic germplasm had the lowest yields. Within years, locations, and harvest systems, the quality‐improved synthetics were nearly always better than the standard cultivars in all measured quality components. The improved synthetics averaged 16 and 13 g kg‐1 lower neutral detergent fiber (NDF) and ADF, respectively, compared to the standard cultivars. The improved synthetics averaged 16, 17, 12, and 3 g kg‐1 higher true digestibility (TD), cell wall digestibility (CWD), CP, and cell wall protein (CWP) concentrations, respectively. Therefore, plants selected for higher nutritive value under a recommended harvest sequence can be developed into synthetics with improved quality when grown under other typical harvest systems.

Rising temperatures due to climate change threaten agricultural crop productivity. As a cool-season crop, wheat is heat-sensitive, but often exposed to high temperatures during the cultivation period. In the current study, a bread wheat panel of spring wheat genotypes, including putatively heat-tolerant Australian and CIMMYT genotypes, was exposed to a 5-day mild (34°C/28°C, day/night) or extreme (37°C/27°C) heat stress during the sensitive pollen developmental stage. Worsening effects on anther morphology were observed, as heat stress increased from mild to extreme. Even under mild heat, a significant decrease in pollen viability and number of grains per spike from primary spike was observed compared with the control (21°C/15°C), with Sunstar and two CIMMYT breeding lines performing well. A heat-specific positive correlation between the two traits indicates the important role of pollen fertility for grain setting. Interestingly, both mild and extreme heat induced development of new tillers after the heat stress, providing an alternative sink for accumulated photosynthates and significantly contributing to the final yield. Measurements of flag leaf maximum potential quantum efficiency of photosystem II (Fv/Fm) showed an initial inhibition after the heat treatment, followed by a full recovery within a few days. Despite this, model fitting using chlorophyll soil plant analysis development (SPAD) measurements showed an earlier onset or faster senescence rate under heat stress. The data presented here provide interesting entry points for further research into pollen fertility, tillering dynamics, and leaf senescence under heat. The identified heat-tolerant wheat genotypes can be used to dissect the underlying mechanisms and breed climate-resilient wheat.