Disease Of Alfalfa Research Articles

Associations among Forage Quality Traits, Vigor, and Disease Resistance in Alfalfa

Major objectives for alfalfa (Medicago sativa L.) breeding include improving forage quality and levels of disease resistance. Little is known about the associations between forage quality characteristics, including pectin (the main component of neutral detergent‐soluble fiber [NDSF]), and disease resistance and vigor in alfalfa. Our objectives were to determine, in two alfalfa populations, the (i) correlations among NDSF and other forage quality traits; (ii) correlations of forage quality traits with plant persistence, vigor, and levels of resistance to diseases; and (iii) heritabilities and expected gains from selection for the aforementioned traits. Simple, phenotypic, and additive genetic correlation coefficients were estimated from half‐sib (HS) progeny tests of two alfalfa populations (NY9505 and NY9515). In both populations, NDSF was negatively correlated with acid detergent fiber (ADF), lignin, and neutral detergent fiber (NDF), and positively correlated with true in vitro dry matter digestibility (IVDMD). Vigor was positively correlated with ADF, lignin, and NDF, and negatively correlated with IVDMD and crude protein (CP) only in NY9515. Of 144 correlation coefficients computed between forage quality traits and resistances to five major alfalfa diseases, only six were significant, and they were low in magnitude (−0.22 ± 0.11 to 0.30 ± 0.14). In an alfalfa improvement program, selection for forage quality is not expected to indirectly affect levels of disease resistance, but it may reduce vigor.

Production of antifungal compounds by Pseudomonas aeruginosa K-187 using shrimp and crab shell powder as a carbon source

In addition to two bifunctional chitinases/lysozymes previously produced, Pseudomonas aeruginosa K-187 grown aerobically in a shrimp and crab shell powder medium produced anti-fungal compounds that in tests effectively inhibited 36 strains of fungi. Maximum inhibitory activity was obtained when P. aeruginosa K-187 was grown aerobically in a medium consisting of 4.75% shrimp and crab shell powder, 0.75% carboxymethyl cellulose, 0.1% K 2HPO 4, 0.05% MgSO 4 7H 2O, 0.3% NaCl, and 0.35% yeast extract at a pH of 6.0. The crude fungicide obtained from the culture broth of P. aeruginosa K-187 retained more than 90% of its inhibitory activities to Fusarium oxysporum even after being treated at a pH of 3 or 100°C for 30 min. It also caused hyphal swelling and lysis in Fusarium oxysporum, a fact that might contribute to its suppression of damping-off disease in alfalfa caused by F. oxysporum.

Infection of alfalfa pollen bySclerotinia sclerotiorum

Blossom blight, caused bySclerotinia sclerotiorum, has become an important disease of alfalfa (Medicago sativa L.) in seed production areas of western Canada. Studies using light microscopy and scanning and transmission electron microscopy revealed that pollen grains of alfalfa are susceptible to infection byS. sclerotiorum. Ascospores ofS. sclerotiorum germinated readily in water with or without pollen grains. Examinations of ascospore—pollen mixtures incubated at room temperature (20–22°C) for 5 days revealed that numerous pollen grains were infected byS. sclerotiorum by direct hyphal penetration through the equatorial germinative pores or through the exine and intine layers of the pollen wall without the formation of infection cushions or appressoria. After penetration, hyphae ramified within the pollen grains, causing plasmolysis of the cytoplasmic membrane and eventual disintegration of the pollen cytoplasm. The study suggests that alfalfa pollen may play a role in the epidemiology of blossom blight in alfalfa.

Root Heave of Alfalfa Cultivars with Differing Levels of Resistance to Aphanomyces Root Rot

AbstractAphanomyces root rot (ARR) (caused by Aphanomyces euteiches Drechs.) and phytophthora root rot (PRR) (caused by Phytophthora sojae M.J. Kaufmann & J.W. Gerdemann) are important diseases of alfalfa (Medicago sativa L.) grown in wet soil, but few studies have quantified the effects of ARR on alfalfa performance. An alfalfa cultivar trial of 82 cultivars with differing levels of ARR resistance was seeded in July 1993 in a naturally infested soil at Marshfield, WI. Excessive precipitation in 1993 and 1994 led to widespread expression of ARR and PRR, and large cultivar yield differences were measured. There was differential root heaving among cultivars in the 1993–1994 winter. Fall 1993 forage yield was low, but cultivars with high ARR resistance yielded >400% more than did susceptible cultivars. Root heaving in 1994 was inversely correlated with level of resistance to ARR (r = −0.68), 1993 forage yield (r = −0.72), and 1994 forage yield (r = − 0.81). Resistant and highly resistant cultivars produced 2 Mg ha−1 more forage than susceptible or low resistance cultivars. Forage yields in 1995 (a relatively dry year) did not differ with ARR resistance level. Under wet soil conditions, ARR‐resistant alfalfa cultivars can produce higher forage yields than susceptible cultivars. In addition, resistance to ARR reduces damage due to root heaving.

A kinase-encoding gene from Colletotrichum trifolii complements a colonial growth mutant of Neurospora crassa.

Colletotrichum trifolii is a fungal pathogen which is responsible for anthracnose disease of alfalfa. To initiate research on molecular communication in this fungus, a kinase-encoding gene (TB3) and the corresponding cDNA were cloned and sequenced. The deduced amino acid sequence of TB3 closely resembles that of a Neurospora crassa serine/threonine protein kinase, COT1, required for hyphal elongation and branching. The C-terminal catalytic domains of TB3 and COT1 are highly conserved but the N-terminal regions are divergent, particularly in the homopolymeric glutamine repeats of TB3. Northern analysis indicated that TB3 expression was highest 1 h after inducing conidial germination and 1 h before germ tubes were first observed. Expression of TB3 transcripts returned to constitutive levels by 4 h after induction of germination. TB3 complemented the cot-I mutant of Neurospora crassa, demonstrating the functional conservation of this kinase between a pathogenic and a saprophytic fungus.

Growth Conditions of Alfalfa for Screening of Resistance to Sclerotinia trifoliorum and Microscopic Observations of Infected Tissues.

Sclerotinia crown and stem rot caused by Sclerotinia tri-foliorum Eriks. is a serious disease of alfalfa (Medicago sativa L.). Alfalfa plants of all ages are susceptible to this disease, but the damage is most severe at the seedling stage. Two experiments were carried out to determine the critical seedling stage and growth conditions under which the resistance was expressed most strongly among varieties and strains of alfalfa. Infected tissues were observed cytologically in individuals of selected SR-strains and commercial varieties. They were inocu-lated with the cultured hyphae of two isolates, one from the Aichi field and the other from the Tochigi field. When alfalfa varieties and strains grown under the low temperature/short day regime were inoculated with Sclerotinia trzfoliorum, all of them showed low survival rates in younger plants less than 6-wk-old, but variable rates in 10-wk-old plants, and the 10-wk-old plants of selected strains survived better than commercial varieties.

Molecular signals during the early stages of alfalfa anthracnose

Colletotrichum trifolii causes anthracnose disease of alfalfa (Medicago sativa). Fungal perception and response to host signals are likely to be crucial in determining whether successful infection occurs. Our research is based on two premises: (i) that early recognition events result in specific responses and these responses determine whether disease occurs and (ii) recognition involves signal exchange between host and pathogen. We have taken two approaches to study this interaction. One is to isolate "important" genes by methods that make no assumption about their products and then to use molecular characterization (e.g., sequence, expression pattern) to identify the biochemical processes involved. Alternatively, known biochemical entities (genes) that function in signal transduction in other organisms are used as heterologous probes or primers. These molecules are then manipulated to determine functional relevance to the host–pathogen. Data is presented from the later approach and we show that calmodulin, protein kinase C, and a novel protein kinase are specifically expressed during the early stages of infection. Key words: protein kinase, calmodulin, fungal infection, host–parasite interaction, fungal gene expression.

Culture conditions that influence accumulation of zwittermicin A by Bacillus cereus UW85.

Bacillus cereus strain UW85 produces an antibiotic, designated zwittermicin A, that is associated with the ability of UW85 to suppress damping-off disease of alfalfa (Medicago sativa) caused by the oomycete pathogen, Phytophthora medicaginis, in a laboratory bioassay. We have identified certain culture conditions that promote or suppress zwittermicin A accumulation by UW85. Maximum accumulation was detected in supernatants of trypticase soy broth cultures after sporulation, which is when cultures of UW85 provide the greatest suppression of damping-off on alfalfa. Inorganic amendments to trypticase soy broth cultures had the following effects on zwittermicin A accumulation and disease suppression: phosphate (50 mM or more) reduced zwittermicin A accumulation and disease suppression; ferric iron (0.25-1.0 mM) enhanced zwittermicin A accumulation and disease suppression; micronutrients (manganese, boron, copper, molybdenum, zinc) had no effect on zwittermicin A accumulation or disease suppression. Cultures of UW85 grown in chemically defined minimal medium supplemented with casein hydrolysate or grown in defined medium containing the minimal requirements for growth supplemented with five amino acids (Gln, Arg, Met, Phe, Ile) accumulated zwittermicin A.(ABSTRACT TRUNCATED AT 250 WORDS)

Alfalfa Cultivar Performance with Differing Levels of Resistance to Phytophthora and Aphanomyces Root Rots

Although Phytophthora root rot (Phytophthora medicaginis [Hansen and Maxwell]; PRR) and Aphanomyces root rot (Aphanomyces euteiches [Drechs]; ARR) have been identified as serious diseases of alfalfa (Medicago sativa L.), research has not been conducted to determine what level of resistance is required to adequately protect the crop. Alfalfa cultivars with various levels of PRR and ARR resistance were evaluated for plant stand and vigor during the seeding year in a naturally infested field at Marshfield, WI, over 3 yr (1990-1992). Plant stands of the susceptible cultivar Saranac averaged 50 % less than the dual resistant germplasm WAPH-1. In 1990, alfalfa stands were reduced from 8 plants/ft of row for the dual resistant germplasm to less than 2 plants/ft of row for Saranac. Average vigor score (1 to 5 = best) for resistant lines was 3.6 compared with 1.8 for susceptible cultivars. In a 1993 study at Marshfield, severe root rot stress occurred, resulting in yield increases of 325 % for cultivars having high resistance (HR) ratings for PRR and ARR compared with the dual susceptible cultivars. Regression equations relating level of PRR or ARR resistance and forage yield were developed from summary data of alfalfa cultivar evaluations conducted at 26 Wisconsin locations. Forage yield increased as the level of PRR resistance increased from 0 to 40 % (susceptible [S] to resistant [R]). Yields of cultivars increased linearly with increasing level of ARR resistance. These data verify that PRR and ARR are serious diseases, especially in wet soils. We recommend that farmers select cultivars classified as R or HR (> 30 % resistance) for both PRR and ARR for adequate crop protection and maximum forage productivity in Wisconsin

Selection for Resistance to Fusarium Root Rot, and Associations among Resistances to Six Diseases in Alfalfa

Fusarium root and crown rot in New York, caused mostly by Fusarium avenaceum (Fr.:Fr.) Sacc., F. oxysporum Sehlechtend.:Fr., and F. solani (Mart.) Sacc., reduces longevity and productivity of alfalfa (Medicago saliva L.). The research objectives were to determine correlations among six alfalfa diseases and progress from recurrent phenotypic selection for resistance to fusarium root rot. From alfalfa half‐sib progenies, phenotypic and additive genetic correlation coetlicients were estimated among resistances to disease caused by the three Fusarium spp. and three common vascular diseases, bacterial wilt (BW) [caused by Clavibacter michiganense subsp, insidiosum (McCall.)], verticillium wilt [caused by Verticillium albo‐atrum (Reinke & Berthier)], and fusarium wilt [caused by F. oxysporum Seh. ex Fr. f. sp. medicaginis (J. L. Weimer)]. Resistances to fusarium wilt (FW) verticillium wilt (VW) were significantly correlated (additive genetic, r = 0.32). Correlations among resistances to the root and crown rot fusaria were moderately to highly positive. Resistances to root rot caused by F. avenaceum and F. solani were moderately and positively correlated with resistance to VW. In two plant populations, two cycles of recurrent phenotypic selection for resistance to root rot species increased levels of resistance by 15 to 44%. Selection for resistance to root rot caused by specific Fusarium species conferred a general resistance to rot caused by all three species, confirming the results of the correlation experiment. Alfalfa populations with resistance to disease caused by the Fusarium spp. can be developed by using an inoculum mixture of all three Fusarium spp., without negative effects on resistances to the vascular diseases.

Biological activities of two fungistatic antibiotics produced by Bacillus cereus UW85.

Cultures and culture filtrates of Bacillus cereus UW85 suppress damping-off of alfalfa caused by Phytophthora medicaginis. We studied the role in disease suppression of two antibiotics from culture filtrates of UW85 that reversibly inhibited growth of P. medicaginis. We purified the two antibiotics by cation-exchange chromatography and high-voltage paper electrophoresis and showed that one of them, designated zwittermicin A, was an aminopolyol of 396 Da that was cationic at pH 7.0; the second, designated antibiotic B, appeared to be an aminoglycoside containing a disaccharide. Both antibiotics prevented disease of alfalfa seedlings caused by P. medicaginis. Purified zwittermicin A reversibly reduced elongation of germ tubes derived from cysts of P. medicaginis, and antibiotic B caused swelling of the germ tubes. Mutants generated with Tn917 or mitomycin C treatment were screened either for antibiotic accumulation in an agar plate diffusion assay or for the ability to suppress damping-off disease of alfalfa. Of 2,682 mutants screened for antibiotic accumulation, 5 mutants were substantially reduced in antibiotic accumulation and disease-suppressive activity. Of the 1,700 mutants screened for disease-suppressive activity, 3 mutants had reduced activity and they accumulated less of both antibiotics than did the parent strain. The amount of antibiotic accumulated by the mutants was significantly correlated with the level of disease suppression. Addition of either zwittermicin A or antibiotic B to alfalfa plants inoculated with a culture of a nonsuppressive mutant resulted in disease suppression. These results demonstrate that B. cereus UW85 produces two fungistatic antibiotics that contribute to suppression of damping-off disease of alfalfa.

Field Response of Alfalfa to Harvest Frequency, Cultivar, Crown Pathogens, and Soil Fertility: II. Crown Rot

AbstractDecline in stand density and productivity of alfalfa (Medicago sativa L.) over time in Canada and the USA has been attributed, in part, to crown and root diseases. In 1985, an experiment was initiated at three locations in Saskatchewan to examine the interaction of (i) harvest frequency, (ii) alfalfa cultivar, (iii) inoculation with fungal crown rot pathogens (Coprinus psychromorbidus, Phoma sclerotioides, or Fusarium spp.), and (iv) K nutrition on the etiology, lesion initiation, incidence, and severity of crown rot of alfalfa. Plant samples were collected from the plots in early spring and late fall each year, starting 1 yr after seeding. The pattern of symptom initiation and lesion expansion were similar at all sites. Lesions were observed initially at the base of senescing stems, and spread laterally into the crown and vertically into the tap root. Lesions were observed on plants at all sites on the first sampling date (> 70% of plants affected at Loon Lake and Saskatoon and 32% at Melfort), but severity was low. By the fall of the following year (1987), incidence was near 100% at all sites, and severity had increased markedly. Harvest frequency and K fertility did not affect crown rot at any location. Inoculation with C. psychromorbidus resulted in small increases in crown rot severity at two sites, but inoculation with the other pathogens had no effect. ‘Nordica’ alfalfa was more resistant to crown rot than ‘Beaver’. These results indicate that resistance to crown rot may be advantageous if long‐term persistence is required, but resistance is not required in short‐term rotations. Also, crown rot and crown bud rot, two alfalfa diseases that have previously been described as distinct entities, appear to be a single disease complex, based on similarities in symptom development and the organisms associated with affected plants.

Development of Foliar Diseases of Alfalfa in Relation to Microclimate, Host Growth, and Fertility

Foliar diseases of alfalfa in four fertility treatments and an untreated control were evaluated in relation to microclimate, host growth, and soil fertility during 1991 and 1992. Over the course of six growth periods, alfalfa growth and disease development varied significantly. Disease incidence and severity were greater on leaves from the lower half of shoots than on leaves from the upper half. Disease development depended on moisture conditions. The relationship of disease to moisture varied between the upper and lower halves of shoots. Disease on the lower half of shoots was correlated with leaf wetness duration as well as atmospheric moisture conditions; disease on the upper half of shoots was correlated only with cumulative rainfall

Potential for Seedling Disease of Alfalfa Caused byAphanomyces euteichesin a Kentucky Soil

Studies were initiated to investigate the potential for seedling disease of alfalfa under controlled conditions in a Kentucky soil naturally infested with Aphanomyces euteiches. Germinated seeds of 21 alfalfa cultivars or experimental lines were planted into pots containing a Heitt silty clay loam and placed in a growth chamber at 24 C for 3 wk. Pots were irrigated with either a 5-μg/ml metalaxyl solution (to control Pythium and Phytophthora spp.) or a solution of 5 μg/ml of metalaxyl + 10 μg/ml of hymexazol (to control A. euteiches also) (.)

Efficiency of Multistage Sampling for Estimation of Intensity of Leaf Spot Diseases of Alfalfa in Field Experiments

In each of two field experiments, efficiency of multistage sampling was evaluated for estimation of intensity of leaf spot diseases during 10 periods of alfalfa growth over 2 yr. Disease was assessed visually on sections of the alfalfa canopy with the aid of descriptive rating scales. In experiment A, severity of disease was assessed every 7 days on four canopy sections (0.5×0.5 m) per replicate plot (3×3 m) with 12 plots per treatment (...)

Seedling and Rootlet Diseases of Forage Alfalfa Caused byPythium irregulare

Isolates of Pythium irregulare caused seedling diseases of alfalfa (Medicago sativa) over a range of temperatures (16-32 C); however, postemergence damping-off and root-forking were most severe at 16 and 21 C. Alfalfa shoot growth was retarded when seedlings were grown in either pasteurized or raw soils amended with culture-grown inocula adjusted to give inoculum densities of propagules within ranges measured in field soils. A negative correlation was found between infection rates of feeder roots by P. irregulare (...)

Quantitative Relationships Between Yield and Foliar Diseases of Alfalfa

Quantitative Relationships Between Yield and Foliar Diseases of Alfalfa

Influence of P and K fertilization on Phytophthora root rot or excess soil water injury of alfalfa cultivars

Abstract Phytophthora root rot (PRR) is an important disease of alfalfa (Medicago sativa L.) in wet soils. Excess soil water (ESW) stress is required for the successful infection and development of PRR. The effects of P at 0, 40, and 80 μg.g‐1 soil and K at 0, 120, and 240 μg.g‐1 soil (in factorial combinations) on the severity of PRR or ESW stress was investigated on a PRR‐susceptible (Iroquois) and a resistant (Oneida) alfalfa cultivar in a greenhouse trial. P and K applications significantly increased the dry weight of tops prior to imposition of PRR or ESW stress. However, plants subjected to PRR or ESW stress did not respond significantly to P or K and there was no significant effect of P or K on the severity of PRR or ESW injury. The plants subjected to PRR or ESW stress had lower tissue P concentration than those under stress‐free conditions. Increasing P additions resulted in a significant increase in P concentration of Iroquois plants, while in Oneida the response was non‐significant. The respons...

Witches' Broom Disease of Alfalfa in Saudi Arabia

Witches' Broom Disease of Alfalfa in Saudi Arabia

Crown and Root Fungal Diseases of Alfalfa in Egypt

Crown and Root Fungal Diseases of Alfalfa in Egypt