Soil‐less bioassays for early screening for resistance to imazapyr in sunflower (Helianthus annuus L.)

BACKGROUND: Rapid and efficient diagnostic tests for early screening of herbicide resistance are convenient alternatives to field screening methods. There is a need for a quick, reliable and cost‐effective method for rapid diagnosis of imidazolinone resistance in sunflower (Helianthus annuus L.). RESULTS: Two seed germination bioassays were developed. Seeds from three sunflower inbred lines differing in resistance to imidazolinones were germinated either on solid culture medium or placed in plastic pots filled with commercial perlite. After 8 days incubation under controlled conditions, both assays successfully distinguished susceptible genotype from the resistant and intermediate ones. The susceptible genotype showed arrested root growth at all herbicide treatments (root length < 1 cm). The resistant genotype developed a complete root system even when exposed to the highest dose of herbicide. However, no definite differences were observed for the intermediate and resistant genotypes with respect to root growth under the different herbicide treatments. CONCLUSION: The simple and rapid screening assays described in the present study were useful in discriminating imidazolinone resistance at the seedling stage. Therefore, these bioassays could be potential tools for early screening of imidazolinone resistance genes from large sunflower populations. Copyright © 2009 Society of Chemical Industry     

Infection process of Phoma koolunga on stem and leaf tissue of resistant and susceptible field pea (Pisum sativum)

This study investigates the infection process of Phoma koolunga on field pea (Pisum sativum) stems and leaves using different susceptible and resistant pea genotypes for each tissue, viz. 05P778‐BSR‐701 (resistant) and 06P830‐(F5)‐BSR‐5 (susceptible) for stems and ATC 866 (resistant) and ATC 5347 (susceptible) for leaves. On both resistant and susceptible genotypes, light and scanning electron microscopy showed P. koolunga conidia infect stem and leaf tissues directly via appressoria or stomatal penetration, but with more infections involving formation of appressoria on stems than on leaves. On leaves of the resistant genotype, at 72 h post‐inoculation, P. koolunga penetrated more frequently via stomata (5.2 conidia per 36 893 μm²) than by formation of appressoria (1.8 conidia); yet no such difference was observed on stems of the resistant genotype. In contrast, at the same time point, the number of conidia infecting the susceptible genotype by formation of appressoria on either stems (135 conidia) or leaves (11.3 conidia) was significantly greater than via stomata (8 and 7.3 conidia, stems and leaves, respectively). Mean germ tube length of germinating P. koolunga conidia on both stems (29.8 μm) and leaves (32.9 μm) of the resistant genotype was less than on the susceptible genotype (40.5 and 63.7 μm, stem and leaves, respectively). In addition, there were differences in the number of germ tubes emerging from conidia on resistant and susceptible genotypes. These are the first insights into the nature of leaf and stem resistance mechanisms operating in field pea against P. koolunga.     

The infection process of Moniliophthora perniciosa in cacao

The development of the basidiomycete Moniliophthora perniciosa in resistant and susceptible Theobroma cacao genotypes was analysed. The infection process leading to broom formation in shoot apexes was characterized by studying the kinetics of basidiospore germination, mode of penetration and colonization of the pathogen. Both resistant and susceptible cacao genotypes were inoculated with M. perniciosa and kept in the greenhouse for 90 days, explants were collected, treated for histological studies and meristematic tissues were observed by electron and light microscopy. Variation in the kinetics of germination between the cacao genotypes was detected 4 h after inoculation. The fungal penetration occurred through the star‐shaped trichome base, natural openings on the cuticular surface and stomata. Host responses between genotypes were found to be different. Compared with non‐infected plants, the swelling of all the stem tissues was evident at 60 days after inoculation. In the susceptible genotype, typical symptoms developed and fungal colonization was more intense than in resistant genotypes, which showed little or no fungal colonization. The investigations reported herein provide an important step in understanding the pattern of pre‐ and post‐penetration events of M. perniciosa in cacao genotypes with different levels of resistance to this disease.     

Seed germination behavior of glyphosate‐resistant and susceptible Italian ryegrass (Lolium multiflorum Lam.)

Ryegrass (Lolium multiflorum Lam.) is one of the most difficult annual weeds to control in cultivation systems worldwide, especially in temperate regions. The widespread use of herbicides in the past two decades has selected resistant biotypes of ryegrass in crops in Southern Brazil. Ryegrass seeds are dormant when disseminated and germination can be staggered over time (crop‐growing season). Knowledge of the germination behavior of seeds from herbicide‐resistant plants has been little studied, but it would be very useful in integrated weed management. Thus, this study aimed to characterize the dynamics of the soil seed bank of two biotypes of L. multiflorum, one glyphosate‐resistant and the other glyphosate‐susceptible, under a no‐tillage system. The treatments were arranged in a bifactorial scheme, using seeds from biotypes (glyphosate‐resistant and glyphosate‐susceptible) with monthly periods of removal from field (one to 12 months). Seeds of each biotype were placed on the soil surface and covered with soil and straw to simulate no‐till conditions. The percentage of germinated, dormant, and dead seeds was evaluated every 30 days. The ryegrass seed bank of glyphosate‐susceptible and glyphosate‐resistant biotypes was reduced to 11 and 15% of dormant seeds, respectively, at the end of 12 months. However, there was no variation in germination, dormancy, and seed mortality between susceptible and glyphosate‐resistant ryegrass. Seeds of glyphosate‐resistant biotype and susceptible showed germination behavior with similar dynamics in the soil over a period of 12 months.     

Agronomic performance of a triazine resistant foxtail millet (Setaria italica (L.) Beauv.)

The agronomic performance of a foxtail millet line resistant to atrazine, obtained through interspecific hybridization between Setaria viridis and S. italica, was compared to that of the original susceptible cultivar of S. italica. In spite of lower grain yields when both were grown in identical conditions, the use of this resistant material is justified because its yield when weeded with atrazine was similar to that of the susceptible cultivar with handweeding. There were no differences in early season growth rates between these lines at cool temperatures.     

Mapping of clubroot (Plasmodiophora brassicae) resistance in canola (Brassica napus)

Clubroot disease, caused by Plasmodiophora brassicae, has become a major problem in the production of cruciferous crops worldwide. In this study, a population of 121 doubled haploid (DH) lines derived from a crossing between a resistant and a susceptible canola (Brassica napus) genotype was subjected to phenotypic and genotypic studies to determine the inheritance and location of the resistance gene(s). After inoculation with pathotype 3 of P. brassicae, the lines showed a 1:1 segregation ratio for resistance, indicating that resistance in this population is controlled by a single gene. Fifteen PCR‐based markers that were known to be linked to clubroot resistance (CR) genes were screened against genomic DNA from parents and resistant and susceptible bulks. Marker GC1680, linked to the CR gene CRa, exhibited polymorphism between the parents and between the resistant and susceptible bulks. CRa target primers were used to amplify fragments from the two parents and the resultant sequences were compared. A high degree of sequence similarity was found between the parents in the nucleotide binding site domain of CRa. In contrast, sequence polymorphisms were detected in the leucine‐rich repeat (LRR) domain. One pair of primers that amplify a band from the LRR region of the resistant parent but not the susceptible parent was used to screen the DH population. Amplicons were obtained from 60 of the 61 resistant lines and two of the 60 susceptible lines; thus, three recombinants were found. Based on these results, a resistance locus linked to CRa was found.     

Screening Luffa germplasm and advanced breeding lines for resistance to Tomato leaf curl New Delhi virus

The two cultivated Luffa species can be severely infected by Tomato leaf curl New Delhi virus (ToLCNDV) with up to 100% yield loss. Here, 52 Luffa genotypes were screened for ToLCNDV resistance after natural field infection. Mean vulnerability index (VI) ranged from 0.00 to 75.33; genotypes IIHR-137 and IIHR-138 had no symptoms (VI 0), 16 genotypes were resistant (VI 0–25), 15 were moderately resistant (VI 26–50), and 19 were moderate to susceptible (VI?>?50). Ten of the most resistant genotypes and five susceptible checks were then challenge-inoculated using whiteflies or sap in an insect-proof net house; only IIHR-137 [L. cylindrica (L.) Roem.] was symptomless (VI 0.00), and 3–5% of plants of IIHR-138 [L. cylindrica (L.) Roem.] and IIHR-Sel-1 [L. acutangula (L.) Roxb.] had only mild symptoms; genotype Arka Prasan was most susceptible (VI 80.96). Asymptomatic plants were confirmed as infected using polymerase chain reaction. Susceptible genotypes rapidly developed leaf curling, then a severe mosaic 10 days post-inoculation. The resistant inbred lines identified are good candidates for a breeding program for ToLCNDV-resistant cultivars.

     

多堆柄锈菌侵染玉米的细胞学及超微结构特征

为明确玉米对多堆柄锈菌Puccinia polysora侵染后病理反应的细胞学特征,利用扫描和透射电镜技术分析了玉米自交系与多堆柄锈菌互作中二者的细胞变化过程。多堆柄锈菌对玉米的侵染主要以直接穿透叶片表皮侵入为主,少量可从气孔和细胞间隙侵入。接种后,病菌夏孢子在感病自交系叶片上快速并大量萌发,在叶表生长蔓延并侵入表皮组织细胞,7 d后形成夏孢子堆;在抗病自交系上,病菌萌发、菌丝生长均受到明显抑制,少量入侵的病菌也由于寄主细胞死亡而导致菌丝和夏孢子干瘪死亡。侵染早期在感病寄主细胞间隙出现菌丝并穿透细胞壁,在胞内产生分枝菌丝,此时寄主细胞结构正常;随着菌丝进一步扩展,叶绿体等结构发生紊乱,被侵染细胞逐渐死亡。在抗病自交系上,接菌24 h后寄主即出现过敏性坏死反应,侵入位点与周围细胞快速坏死,抑制菌丝生长蔓延;叶绿体中清晰可见深色颗粒状物质;72 h后细胞壁外侧产生大量致密的深色结晶体,应为与抗病反应相关的酚类物质。表明抗多堆柄锈菌的玉米材料可能存在2种抗病途径,即寄主与病菌互作中由分子识别引起的免疫反应和病菌侵入后的系统防卫反应。     

Propanil‐resistant barnyardgrass [Echinochloa crus‐galli (L.) Beauv.] in Sri Lanka: Seedling growth under different temperatures and control

Experiments were conducted to (i) evaluate the efficacy of propanil formulations available in Sri Lanka in controlling Echinochloa crus‐galli; (ii) study the seedling growth of propanil‐resistant (R) and ‐susceptible (S) biotypes of the weed under different temperatures; (iii) quantify the level of resistance in R biotypes and; (iv) to suggest alternative control measures for R biotypes. Field studies showed that retail propanil formulations (36% a.i., EC) applied at 2.7 kg a.i. ha^?1 gave less than 30% control of E. crus‐galli collected from several locations of the north dry zone of Sri Lanka. Chemical analysis revealed that there was no adulteration of propanil formulations at the retailer level. Growth studies conducted in controlled environments indicated that per cent germination and seedling growth of R and S biotypes were similar at the day/night temperature regimes imposed. However, per cent germination for plants grown under a 34/31°C (day/night) regime was 27–29% higher compared to those grown at 28/24°C. At the higher temperature regime, R and S biotypes reached the 2–3 leaf stage five days earlier, and the 4–5 leaf stage seven days earlier. The ED₅₀ values from the dose–response experiments indicated that the R biotype was four times more resistant to propanil than susceptible ones. The resistance index (RI) did not vary significantly under different temperature regimes. Quinclorac (25% a.i., SC) applied at 200 g a.i. ha^?1 and bispyribac‐sodium (10% a.i., SC) applied at 30 g a.i. ha^?1 (recommended dosages) successfully controlled propanil‐resistant biotypes of E. crus‐galli. Conversely, oxadiazon and propanil (8% and 23% a.i., EC, respectively) applied at 280 + 805 g a.i. ha^?1 did not result in satisfactory control.     

Effects of R gene‐mediated resistance in Brassica napus (oilseed rape) on asexual and sexual sporulation of Pyrenopeziza brassicae (light leaf spot)

The phenotype of the R gene‐mediated resistance derived from oilseed rape (Brassica napus) cv. Imola against the light leaf spot plant pathogen, Pyrenopeziza brassicae, was characterized. Using a doubled haploid B. napus mapping population that segregated for resistance against P. brassicae, development of visual symptoms was characterized and symptomless growth was followed using quantitative PCR and scanning electron microscopy on leaves of resistant/susceptible lines inoculated with suspensions of P. brassicae conidia. Initially, in controlled‐environment experiments, growth of P. brassicae was unaffected; then from 8 days post‐inoculation (dpi) some epidermal cells collapsed (‘black flecking’) in green living tissue of cv. Imola and from 13 to 36 dpi there was no increase in the amount of P. brassicae DNA and no asexual sporulation (acervuli/pustules). By contrast, during this period there was a 300‐fold increase in P. brassicae DNA and extensive asexual sporulation in leaves of the susceptible cv. Apex. However, when leaf tissue senesced, the amount of P. brassicae DNA increased rapidly in the resistant but not in the susceptible cultivar and sexual sporulation (apothecia) was abundant on senescent tissues of both. These results were consistent with observations from both controlled condition and field experiments with lines from the mapping population that segregated for this resistance. Analysis of results of both controlled‐environment and field experiments suggested that the resistance was mediated by a single R gene located on chromosome A1.     

青海青稞主栽品种(系)对条纹病和云纹病的抗性鉴定

本研究旨在明确青海青稞主栽品种和后备品种对条纹病和云纹病的抗性,以期为抗病育种及田间病害防治提供理论依据。试验采用田间自然病圃法,对青海主栽的30个青稞品种(系)进行了条纹病和云纹病田间抗性鉴定。结果表明,供试青稞品种(系)对2种病害的抗性存在显著差异,但缺乏免疫品种。对条纹病表现高抗的有13个品种(系),占鉴定总数的43.3%,其中主栽品种有3个,即‘门农1号’、‘昆仑13号’、‘巴青1号’。品系17发病率最低。对云纹病表现高抗的有品系1、品系2、品系6、品系17、品系28、RQKQ-3、RQKQ-5、RQKQ-6、RQKQ-7、RQKQ-8、‘门农1号’、‘互青2号’、‘北青6号’和‘昆仑10号’,共14个,其病情指数均在10以下;表现中抗的共有8个,分别为品系5、品系11、RQKQ-1、RQKQ-9、‘巴青1号’、‘北青3号’、‘北青7号’和‘昆仑13号’。     

Natural variation of Medicago truncatula resistance to Aphanomyces euteiches

We analysed the resistance variation in 14 natural populations of Medicago truncatula from Tunisia to Aphanomyces euteiches infection. The reaction of M. truncatula lines to A. euteiches infection varied from susceptibility to full resistance. Of the overall level of phenotypic variation, 65.4 % was found to occur within populations. Principal component analysis showed a high spread of lines belonging to the same population, indicating no clear structure in the Tunisian M. truncatula populations and supporting the hypothesis of gene flow among populations. Likewise, there was no association between local resistance composition and the geographical distances between populations, ruling out isolation by distance as an explanation. Furthermore, significant correlations were observed between quantitative traits and ecological factors consistent with the local adaptation hypothesis. A cluster analysis of the populations showed the presence of three groups. The first group comprised the populations originating from the centre of the country, containing the main resistant lines. The second group included the populations collected in the south and the mountain region of Thala and contained the main partially resistant lines. The third group comprised the populations sampled from the north regions and saline soils and included the main susceptible lines. Overall, we found that the natural M. truncatula lines were more likely to be susceptible (71.3 %) than resistant (28.7 %) to A. euteiches attack. Nevertheless, many resistant lines exhibiting new reaction patterns to A. euteiches attack were identified in the natural populations and these can be used for the identification of potentially new resistance genes.     

Virulence and inoculum density‐dependent interactions between clubroot resistant canola (Brassica napus) and Plasmodiophora brassicae

To mitigate the impact and dissemination of clubroot in western Canada, canola (Brassica napus) producers have relied on clubroot resistance traits. However, in 2013 and 2014, new strains of the clubroot pathogen, Plasmodiophora brassicae, emerged that are virulent on most clubroot‐resistant (CR) canola genotypes. Novel strains of the pathogen were inoculated onto two susceptible canola cultivars, one resistant line and six CR cultivars. Although all cultivars/lines showed a susceptible response to inoculation with the new strains of P. brassicae, the severity of disease reaction, root hair infection rates and the amount of P. brassicae DNA present in each canola genotype varied depending on the strain. In addition, the effect of inoculum density on disease severity and gall formation was recorded for one of these new strains on a universally susceptible Chinese cabbage cultivar and one susceptible and 10 resistant canola genotypes. Although root galls were observed at an inoculum density of 10³ spores per mL of soil, clear differentiation of susceptible and resistant reactions among canola cultivars/lines was not observed until the inoculum density reached 10⁵ spores mL^?1. At a spore density of 10⁶ spores mL^?1 and above, all cultivars/lines developed susceptible reactions, although there was some differentiation in the degree of reaction. This study shows the potential to develop a unique disease profile for emergent clubroot pathotypes and shows a useful range of spore densities at which to study new P. brassicae strains.     

Histological responses of host and non-host plants to <Emphasis Type="Italic">Hyaloperonospora parasitica</Emphasis>

Differences in Hyaloperonospora parasitica development and plant tissue responses were compared for 10 cruciferous hosts (including both resistant and susceptible genotypes), 3 leguminous and 1 graminaceous non-host species. Cotyledons, or true leaves in the case of Triticum aestivum and Pisum sativum, were studied at 2, 8, 24 h and 3, 5, 7 days post inoculation (dpi). The high levels of zoosporangial germination observed on all species tested, as well as on glass slides, suggested that inhibition of germination did not play a significant role in distinguishing host versus non-host resistance. During the early stages of infection, at spore germination and host penetration, there was no evidence of a clear-cut difference between Brassica host species which displayed a hypersensitive, partially resistant or susceptible reaction compared with non-host species. Haustoria formation was the key infection phase for the establishment of biotrophy. Across all tested species, haustoria were initiated inside the epidermal cells. However, there were significant differences in the frequency and timing of haustorial formation and the final size of haustoria among the tested species at early infection stage. Fully developed haustoria were never observed in Raphanus raphanistrum, Triticum aestivum, Lupinus angustifolius nor Trifolium subterraneum. Instead, the haustorium development appears to abort in the penetrated epidermal cells of these species. Although haustoria were formed in the epidermal and mesophyll cells of Sinapsis alba and Pisum sativum, subsequent hyphal growth and/or continued haustoria formation were rare or few, respectively. Hypersensitive reaction was the key resistance response observed among the host and non-host resistant species tested. It is noteworthy that, in the initial stages of pathogenesis, there was no differentiating point that separated the non-host species from those that were hosts.     

Evaluation of Parameters Accounting for Phomopsis Resistance Using Natural Infection and Artificial Inoculation on Recombinant Inbred Lines From a Cross Between Susceptible and Resistant Sunflower

HA89, a sunflower line susceptible to Phomopsis, was crossed with a resistant line, LR4-17. Two hundred and forty-one F2/F3 progenies and 232 recombinant inbred (RI) lines were derived from this cross. F2/F3 progenies were tested in semi-natural infections in 1994. F7, F8 and F9 were tested with semi-natural infections in 1997, 1998 and 1999, respectively. F7 RI lines were artificially infected with Phomopsis mycelium on leaves in 1997. Family effects were significant in F2/F3 progenies for attack rates on stems and encircling spots rates on stems after semi-natural infections. Line effects were significant for attack rates on stems and encircling spot rates in F7 and F8. F7 RI lines showed a high heritability for speed of necrosis on leaf blades after artificial infection. Continuous and unimodal distributions were observed for attack rates on stems in all experiments done in semi-natural conditions. In contrast, speed of necrosis on leaf blades showed a bimodal distribution. Significant rank correlations were observed between the speed of necrosis on leaf blades and the attack rates on stems. It is suggested that resistance to Phomopsis is the consequence of several mechanisms, independently inherited. It was concluded that speed of necrosis on leaf blades in artificial infections and attack rates on stems in natural infections should be retained as parameters for quantitative trait locus mapping of Phomopsis resistance.     

The effect of timing of fungicide applications on control of frogeye leaf spot and grain yield of soybeans

Soybean cultivar Samsoy 1, and the breeding lines TGx 849-313D and TGx 996-26E, grown in a field with a heavy epidemic of frogeye leaf spot caused byCercospora sojina, were treated with double foliar applications of the fungicide benomyl. The treatments were made using four application schedules at six different growth stages, starting from V₃ (fully developed leaves, beginning with trifoliate nodes) to R₅ (beginning seed_, to determine the effect of the fungucide timing on frogeye leaf spot severity, soybean grain yield and grain quality. Generally, applications at R₁ (beginning bloom) and R₃ (beginning pod) significantly (P<-0.05) reduced disease severity in the 2 susceptible genotypes, Samsoy 1 and TGx 849-313D. Plot yields of these genotypes were also significantly greater than the untreated controls when the fungicide applications were made at R₁ and R₃. There was no significant difference in diseave severity or grain yield, between the untreated control and the different times of application, on the resistant genotype TGx 996-26E. Improved seed germination and lower levels of seed infection byC. sojina occurred for all fungicide timings in the susceptible genotypes. The results suggest that fungicide spraying initiated at R₁ and followed up at R₃ is most effective in frogeye leaf spot control and can also result in higher grain yields, than applications made earlier or later in the season. Control of frogeye leaf spot, however, is best achieved by growing resistant cultivars.     

Resistance and systemic dispersal of Xanthomonas fragariae in strawberry germplasm (Fragaria L.)

The angular leaf spot disease caused by Xanthomonas fragariae is an important plant disease with major impact for the strawberry nursery industry. Currently there is no plant protection product available for controlling the disease effectively. Planting of resistant cultivars seems to be promising, but all commercially used cultivars are susceptible and no donor with a high level of resistance has yet been found. Therefore, a total of 145 genotypes from the Fruit Genebank Dresden (Germany) were evaluated for resistance to X. fragariae by artificial inoculation. Six genotypes were classified as partly resistant, out of which only two (US4808 and US4809) are octoploid. Fragaria vesca f. alba, Fragaria nilgerrensis ‘Yunnan’, F. vesca ‘Illa Martin’ and F. moschata ‘Bauwens’ were also classified as partially resistant, but they are only of limited use for breeding because of their variable ploidy level. Fully resistant genotypes could not be detected. The systemic dispersal of the bacteria in strawberry plants was investigated after inoculation of leaves with X. fragariae strain XF3.9.C and the GFP‐tagged strain XF3.9.C_(pKAN). The systemic spread was evaluated after 3, 7, 14 and 28 days post‐inoculation (dpi) by nested PCR and fluorescence microscopy. After 3 dpi, X. fragariae could be found in all tissues tested including the inoculated leaf, its petiole, the rhizome, the heart bud up to the youngest fully expanded leaf and its petiole. The systemic spread was also detectable in partially resistant genotypes.     

Resistance to Root-knot Nematodes (Meloidogyne spp.) in Vegetable Crops

Abstract

The development of root-knot nematode resistant vegetable varieties has provided an alternative control method to chemical and crop rotation. The term resistance is discussed. Work on 18 vegetables is reviewed.

Thirty tomato strains resistant to one or more Meloidogyne sp. are listed, there was a marked absence of reports on varieties resistant to M. hapla. Several workers have observed resistance in some cultivated and wild Solanum spp. The resistance could be increased by further sib and backcrossing experiments. Eggplant varieties tested for resistance to Meloidogyne spp. showed varying degrees of resistance in about 14 varieties. Further backcrossing studies between Solanum melongena and S. sysimbrifolium could provide useful results. Tests on resistance to nematodes in pepper have revealed many resistant varieties. All the pepper varieties tested were susceptible to M. hapla. The nature of resistance in sweet potato has been studied. Some varieties of Cucumis spp. have been found to be resistant to Meloidogyne spp. Since no resistance was found in C. melo, these wild species could be used in the development of a commercial muskmelon variety. Tests with 83 watermelon varieties indicated that all varieties were resistant to M. hapla. It was difficult to find resistance to Meloidogyne spp. in Cucurbita, but tests on wild species have yet to be carried out. Work on lima bean, snap bean, pea, soyabean, cowpea and broadbean has produced a limited number of resistant vegetable varieties, which are described. Since resistance patterns in plants may change under different environmental or biological conditions, it is essential to test varieties under these conditions for a long period before they are released for commercial cultivation. The advantages of using resistant vegetable varieties, as compared with other methods of pest control, are outlined.     

Impact of <Emphasis Type="Italic">Sugarcane yellow leaf virus</Emphasis> on growth and sugar yield of sugarcane

A survey revealed that Sugarcane yellow leaf virus (SCYLV) is found on all Hawaiian sugarcane plantations including those where no yellow leaf symptoms were observed. In a comparison of growth and yield between SCYLV-infected and SCYLV-free plants of the cultivar H87-4094, germination and early shoot growth of infected plants were retarded. The number of stalks per stool was reduced by 30%, biomass was reduced by 29%, and sugar yield by 26% when plants were harvested after 11 months. Yields did not decrease when plants were harvested after 2 years. Thus, SCYLV could reduce yield, even when the plants were asymptomatic. In a field test of SCYLV-susceptible (infected) and -resistant cultivars to compare growth and yield, 10 commercial cultivars (six susceptible and four resistant to SCYLV) were grown in eight fields with different climates and soils. Primary stalk length, biomass and sugar yield did not differ between susceptible and resistant cultivars under any field conditions. Thus, harmful effects of SCYLV on yield cannot be deduced by comparing different cultivars.     

Germination and seedling emergence of glyphosate‐resistant and susceptible biotypes of goosegrass (Eleusine indica[L.] Gaertn.)

Effects of environmental factors on the germination and seedling emergence of glyphosate‐resistant (R) and ‐susceptible (S) biotypes of Eleusine indica (L.) Gaertn. were examined under laboratory and greenhouse conditions. The R biotype exhibited a higher germination percentage compared with the S biotype at constant temperatures of 20 and 35°C under dark conditions, and alternating temperatures of 30/25°C, and 35/25°C during a 12 h photo period. For both biotypes, germination was optimal at alternating temperatures of 30/20°C and 35/20°C. However, there was no significant difference (P > 0.05) in the germination between the R and S biotypes at these temperature regimes. The germination of both biotypes was inhibited by osmotic stress imposed by a water potential of ?0.80 MPa. When the moisture stress was released and the seeds were subsequently transferred to distilled water, the germination was enhanced to approximately 90% and 16% for the R and S biotype seeds, respectively. Higher emergence rates were obtained in shallow seed depths (0 or 2 cm) compared to deep depths. Emergence percentage of the R biotype was higher than that of the S biotype at 0 cm and 2 cm depths. The maximum emergence percentage of the R biotype was higher than that of S biotype when seeds were sown on the surface of either loamy or clay loam soil taken from three different sites.