Joseph P. Yenish

Single nucleotide mutation in the barley acetohydroxy acid synthase (AHAS) gene confers resistance to imidazolinone herbicides

Induced mutagenesis can be an effective way to increase variability in self-pollinated crops for a wide variety of agronomically important traits. Crop resistance to a given herbicide can be of practical value to control weeds with efficient chemical use. In some crops (for example, wheat, maize, and canola), resistance to imidazolinone herbicides (IMIs) has been introduced through mutation breeding and is extensively used commercially. However, this production system imposes plant-back restrictions on rotational crops because of herbicide residuals in the soil. In the case of barley, a preferred rotational crop after wheat, a period of 9–18 mo is required. Thus, introduction of barley varieties showing resistance to IMIs will provide greater flexibility as a rotational crop. The objective of the research reported was to identify resistance in barley for IMIs through induced mutagenesis. To achieve this objective, a sodium azide-treated M2/M3 population of barley cultivar Bob was screened for resistance against acetohydroxy acid synthase (AHAS)-inhibiting herbicides. The phenotypic screening allowed identification of a mutant line showing resistance against IMIs. Molecular analysis identified a single-point mutation leading to a serine 653 to asparagine amino acid substitution in the herbicide-binding site of the barley AHAS gene. The transcription pattern of the AHAS gene in the mutant (Ser653Asn) and WT has been analyzed, and greater than fourfold difference in transcript abundance was observed. Phenotypic characteristics of the mutant line are promising and provide the base for the release of IMI-resistant barley cultivar(s).

Winter wheat competition against jointed goatgrass (Aegilops cylindrica) as influenced by wheat plant height, seeding rate, and seed size

Abstract Jointed goatgrass is a troublesome weed in winter wheat with selective control only possible with a herbicide-resistant crop. Even with herbicide-resistant wheat, cultural control is still an important part of jointed goatgrass management. A study was conducted in 1998 and 2000 to determine whether using larger sized seed of a tall wheat variety at an increased seeding rate would reduce the effect of jointed goatgrass on winter wheat. Wheat seed size, seeding rate, and variety height had no effect on jointed goatgrass plant density. Tall (∼130 cm) wheat reduced mature jointed goatgrass biomass 46 and 16% compared with short (∼100 cm) wheat in years 1 and 2 of the experiment, respectively. Spikelet biomass was also reduced approximately 70 and 30% in the same respective years. One thousand–spikelet weight of jointed goatgrass was reduced 37 and 7% in years 1 and 2, respectively, when grown in competition with taller compared with shorter wheat. Moreover, dockage was 80 and 30% less in years 1 and 2, respectively, when grown in competition with taller than shorter wheat. Mature jointed goatgrass height was similar regardless of the competitive wheat height. However, jointed goatgrass was as much as 18% taller than the short wheat and 15% shorter than the tall wheat. Seeding rate had the most consistent effect on wheat yield. Wheat seed yield was about 10% greater with 60 than 40 seed m−1 of row when competing with jointed goatgrass. Results of this study indicate that growers could use a tall winter wheat variety to improve crop competition against jointed goatgrass. Results also indicate that plant breeders should consider plant height because herbicide-resistant varieties are developed for the integrated management of jointed goatgrass. Nomenclature: Jointed goatgrass, Aegilops cylindrica Host. AEGCY; winter wheat, Triticum aestivum L. ‘Nugaines’.

Inheritance and physiological basis for 2,4-D resistance in prickly lettuce (Lactuca serriola L.).

Experiments were conducted to determine the inheritance and physiological basis for resistance to the synthetic auxinic herbicide (2,4-dichlorophenoxy)acetic acid (2,4-D) in a prickly lettuce biotype. Inheritance of 2,4-D resistance in prickly lettuce is governed by a single codominant gene. Absorption and translocation were conducted using (14)C-2,4-D applied to 2,4-D-resistant and -susceptible biotypes. At 96 h after treatment (HAT), the resistant biotype absorbed less applied 2,4-D and retained more 2,4-D in the treated portion of the leaf compared to the susceptible biotype. The resistant biotype translocated less applied 2,4-D to leaves above the treated leaf and crown at 96 HAT compared to the susceptible biotype. No difference in the rate of metabolism of 2,4-D was observed between the two biotypes. Resistance to 2,4-D appears to originate from a reduced growth deregulatory and overstimulation response compared to the susceptible biotype, resulting in lower translocation of 2,4-D in the resistant prickly lettuce biotype.

Feral Rye (Secale cereale) in Agricultural Production Systems

Feral rye, commonly referred to as cereal, winter, common, or volunteer rye, is an important weed in winter wheat production in many parts of the United States and the world. Feral rye reduces net profits in the United States by more than

EST-SSR Development from 5 Lactuca Species and Their Use in Studying Genetic Diversity Among L. serriola Biotypes

27 million due to lower grain yields, increased dockage, and reduced land values. To date, limited research has been conducted on components that make feral rye a problem in various cropping systems. Herbicide-tolerant wheat technology can be used to manage feral rye, but current efficacy levels are not adequate for high feral rye densities. In addition, the long-term effects that individual management strategies may have on feral rye populations are unknown. This review addresses the physical, environmental, and genetic characteristics of Secale cereale. Current economic impact, management, and research data gaps are also discussed. Nomenclature: Feral rye, Secale cereale L. #3 SECCE; wheat, Triticum aestivum L. Additional index words: Integrated pest management, winter wheat, winter annual grasses, best management practices.

Vernalization response of plants grown from spikelets of spring and fall cohorts of jointed goatgrass

Prickly lettuce (Lactuca serriola L.) is a problematic weed of Pacific Northwest and recently developed resistance to the auxinic herbicide 2,4-D. There are no publically available simple sequence repeat (SSR) markers to tag 2,4-D resistance genes in L. serriola. Therefore, a study was conducted to develop SSR markers from expressed sequence tags (ESTs) of 5 Lactuca species. A total of 15,970 SSRs were identified among 57,126 EST assemblies belonging to 5 Lactuca species. SSR-containing ESTs (SSR-ESTs) ranged from 6.23% to 7.87%, and SSR densities ranged from 1.28 to 2.51 kb(-1) among the ESTs of 5 Lactuca species. Trinucleotide repeats were the most abundant SSRs detected during the study. As a representative sample, 45 ESTs carrying class I SSRs (≥ 20 nucleotides) were selected for designing primers and were also searched against the dbEST entries for L. sativa and Helianthus annuus (≤ 10(-50); score ≥ 100). In silico analysis of 45 SSR-ESTs showed 82% conservation across species and 68% conservation across genera. Primer pairs synthesized for the above 45 EST-SSRs were used to study genetic diversity among a collection of 22 L. serriola biotypes. Comparison of the resultant dendrogram to that developed using phenotypic evaluation of the same subset of lines showed limited correspondence. Taken together, this study reported a collection of useful SSR markers for L. serriola, confirmed transferability of these markers within and across genera, and demonstrated their usefulness in studying genetic diversity.

Resistance of a Prickly Lettuce (Lactuca serriola) Biotype to 2,4-D

Abstract Jointed goatgrass is most commonly described as a winter annual species. However, it has been observed to produce spikes in spring crops, apparently without being exposed to vernalizing conditions. A controlled environment study was conducted to determine the reproductive response of jointed goatgrass plants grown from seeds of fall- and spring-emerging parent plants to various vernalization durations. Winter wheat was included as a control. Winter wheat spikelet production was dependent on vernalization, and the number of spikes per plant was 10-fold greater if the plants were exposed to 4 C for 10 wk. In contrast, jointed goatgrass spike production without vernalization remained as high as 50% of that produced by plants exposed to 10 wk of vernalization conditions. Jointed goatgrass is thus not as dependent on vernalization for reproduction as the comparative winter wheat standard. Apparently, jointed goatgrass is more a facultative rather than an obligate winter annual. Rotating to a spring-seeded crop should not be expected to completely prevent jointed goatgrass seed production. Fields rotated to spring wheat to eliminate jointed goatgrass seed production should be monitored, and jointed goatgrass should be hand pulled or otherwise controlled to ensure zero seed production. Nomenclature: Jointed goatgrass, Aegilops cylindrica L. AEGCY; winter wheat, Triticum aestivum L. ‘Madsen’.

The Critical Period of Weed Control in Lentil (Lens culinaris) in the Pacific Northwest

Abstract Dose-response experiments were conducted on a biotype of prickly lettuce collected from Whitman County, WA, to determine the level of resistance to 2,4-D. Initially, progeny of prickly lettuce that survived two applications of glyphosate and 2,4-D in mixture were collected to determine if antagonism of the 2,4-D or glyphosate was occurring. Prickly lettuce survival was determined to not be due to antagonism of 2,4-D or glyphosate when the two herbicides were applied in mixture. The doses required to reduce growth 50% (GR50) for resistant and susceptible field-collected prickly lettuce were 150 and 6 g ae/ha 2,4-D, respectively, indicating the resistant biotype was 25 times more resistant to 2,4-D than the susceptible biotype. The resistant biotype expressed injury but produced regrowth following application. A dose of 2,4-D at 220 g/ha was required to reduce regrowth frequency 50% (FR50) for resistant field-collected prickly lettuce. Regrowth was also observed with the susceptible biotype, although the FR50 was much lower (10 g/ha), resulting in an R/S ratio of 22 based on the respective FR50 values. A rate of 4,300 g/ha 2,4-D (10 times the maximum labeled rate in wheat) was required to reduce the regrowth frequency in the resistant biotype to zero. Nomenclature: 2,4-D; glyphosate; prickly lettuce, Lactuca serriola L. LACSE; wheat, Triticum aestivum L.

Influence of glyphosate, crop volunteer and root pathogens on glyphosate-resistant wheat under controlled environmental conditions.

Abstract The critical period of weed control (CPWC) for ‘Pardina’ and ‘Brewer’ lentil was determined in field experiments near Pullman, WA, in 2008 and 2009. Trial treatments were kept either weed free for periods of 0, 14, 25, 35, 45, 60, 75, or ∼90 d after emergence (DAE), or weeds were allowed to grow before removal for periods of 0, 14, 25, 35, 45, 60, 75, or ∼90 DAE. Averaged across varieties, lentil with season-long weed interference had 29.5 and 32% seed yield reduction compared to weed-free lentils in 2008 and 2009, respectively. When measured at crop maturity, a 1% loss in lentil seed yield resulted from each 5.68 g m−2 of dry weed biomass. Based on a 5% yield loss threshold, the CPWC for lentil was estimated to be from 270 to 999 growing degree days (GDD), 22 to 57 DAE, or crop growth stage (CGS) 7 to the early pod stage during 2008. In 2009, the CPWC was 624 to 650 GDD, with no occurrence of a CPWC when estimated using DAE and CGS. Spiny sowthistle emerged and competed with the lentil crop later in the growing season than mayweed chamomile, indicating that mayweed chamomile may be an earlier and stronger competitor than spiny sowthistle. Nomenclature: Mayweed chamomile, Anthemis cotula L.; prickly lettuce, Lactuca serriola L.; spiny sowthistle, Sonchus asper (L.) Hill; lentil, Lens culinaris Medik. ‘Pardina’ and ‘Brewer’.

Herbicide-Resistant Grass Weed Development in Imidazolinone-Resistant Wheat: Weed Biology and Herbicide Rotation'

BACKGROUND The herbicide glyphosate has a synergistic effect on root disease because of increased susceptibility from reduced plant defenses resulting from the blockage of the shikimic acid pathway. Could glyphosate-resistant (GR) wheat cultivars and glyphosate application in-crop increase the risk of damage from soil-borne pathogens? Growth chamber experiments were conducted with two GR wheat lines and their corresponding glyphosate-sensitive (GS) parents and four pathogens (Rhizoctonia solani Kühn R. oryzae Ryker & Gooch, Gaeumannomyces graminis (Sacc.) v. Arx & J. Olivier var. tritici J. Walker and Pythium ultimum Trow). Treatments consisted of different herbicide timings and planting of crop volunteer to mimic management practices in the field. RESULTS GR cultivars were not inherently more susceptible to root pathogens than GS cultivars, and application of glyphosate did not increase root disease. When crop volunteer was grown in close proximity to GR cultivars, the timing of glyphosate application had a profound effect. In general, the longer the crop volunteer was left before killing with glyphosate, the greater was the competitive effect on the planted crop. Both R. solani and G. graminis var. tritici reduced plant height, number of tillers and root length of the GR cultivars in the presence of crop volunteer with glyphosate application. CONCLUSION To minimize the damaging effects of these pathogens, producers should apply glyphosate at least 2-3 weeks before planting GR wheat, as currently advised for GS cereals.