Diaporthe Phaseolorum Research Articles

Physiologic Specialization of Diaporthe phaseolorum var. caulivora in Soybean

Physiologic Specialization of Diaporthe phaseolorum var. caulivora in Soybean

Evidence for homothallism and vegetative compatibility in southern Diaporthe phaseolorum

Twenty-nine vegetative compatibility groups (vcgs) were identified among 297 isolates of the fungus causing soybean stem canker in the southeastern United States (southern Diaporthe phaseolorum). Of the isolates characterized, 79% were from one of the vcgs described (group 1). Barrage zones formed between isolates from different vcgs when grown on potato dextrose agar, and also formed, but not always distinctly, on cornmeal agar, Czapek-Dox agar, lima bean agar, and malt agar; barrages did not form on Sach's agar or water agar. Two types of evidence suggested that southern D. phaseolorum is homothallic. Perithecia and viable ascospores were produced by single ascospore isolates, and ascospores produced by mass isolates were always of the same compatibility group as the parental mass isolate.

Yield Reductions Caused by Stem Canker in Soybean1

Stem canker (caused by Diaporthe phaseolorum var. caulivora Athow & Caldwell) was first observed in Louisiana on soybean [Glycine max (L.) Merr.] near Rosa in 1981. In 1982, several thousand hectares of soybeans were damaged in the southern part of Louisiana, some of which were heavily damaged. The objective of this study was to assess the extent of yield reductions of soybean cultivars caused by stem canker in Louisiana. Thirty‐two cultivars were field grown in Olivier silt loam (fine‐silty, mixed, thermic Aquic Fragiudalfs) soil. They were grown in a randomized complete block design with four replications. A wide range of responses was observed; several cultivars from Maturity Groups V through VIII were resistant to the disease. Significant negative correlations occurred between yield and disease ratings among cultivars and maturity groups. This study indicated several cultivars that should not be grown in soil where the stem canker organism is known to be present and identified other cultivars that could possibly be grown in the presence of the stem canker organism.

Some observations on the ascospore and cultural morphology ofDiaporthe phaseolorumf. sp.caulivora, cause of soybean stem canker

Ascospores of Diaporthe phaseolorum f. sp. caulivora from perithecia produced on cankered stems grown in Alabama, Georgia, and Maryland were broadly fusiform, usually inequilateral or slightly curved, bicellular with two guttules per cell, hardly or not at all constricted at the septum, 7.5-10.5 × 2.0-2.7 μm. Perithecia on a few cankered stems from Alabama and Georgia produced ascospores that resembled type material, that is, they were elongate-ellipsoidal and slightly constricted at the septum, but were smaller, 4.4-6.3 × 1.6-2.1 μm, compared to 8.6-11.8 × 3.0-3.9 μm. When cultured on potato dextrose agar, ascospores of both types produced only pycnidia of Phomopsis phaseoli, the anamorph of D. phaseolorum.

A New Phomopsis Species from Soybean

A new species of Phomopsis isolated from soybean is described. The species, P. longicolla, differs from P. sojae, the anamorph of Diaporthe phaseolorum var. sojae, in several morphological characte...

Seed molds of soybean in Ontario and the influence of production area on the incidence ofDiaporthe phaseolorumvar.caulivoraandPhomopsissp.

Diaporthe phaseolorum var. caulivora (Dpc) and Phomopsis sp. (Ps) were the predominant pathogens isolated from 328 pedigreed seed lots of soybean (Glycine max) produced in Ontario in 1980, 1981, and 1982. Dpc and/or Ps were present in 89% of the seed lots. Mean incidence of Ps in 1981 and 1982 was higher in seed of the cultivar Harcor produced in an area having a longer growing season than required for cultivar maturity, but mean incidence of Ps in seed lots of the cultivar Hodgson was similar in all production areas. Incidence of Dpc was not affected by area of production. Sclerotinia sclerotiorum was isolated from surface sterilized seed of one seed lot in 1982. Ten other fungi were found infrequently in seed lots.

Inheritance of Reaction to Stem Canker in Soybean1

There are no known published reports concerning the inheritance of reaction to the disease stem canker [caused by the fungus Diaporthe phaseolorum (Cke. & Ell.) Sacc. var. caulivora Athow & Cald.] in soybean [Glycine max (L.) Merr.]. Because stem canker has become a serious soybean disease in the southern United States, and because a source of resistance has been identified, information on the inheritance of reaction to this disease is needed. The objective of this study was to determine the inheritance of resistance to stem canker found in the soybean ‘Tracy‐ M.’ Crosses were made between Tracy‐M and a very susceptible line, J77‐339. The disease reactions of parental, F1, F2 and F3 populations from that cross to stem canker were studied under field conditions to determine the genetic basis for resistance. All F1 plants were resistant and the F2 generation fit a 15 resistant:1 susceptible ratio (✕2 probability = 0.75 to 0.90). The 199 F, families fit a ratio of 7 resistant:8 segregating:! susceptible (X2 probability = 0.25 to 0.50). These results indicate that stem canker resistance in Tracy‐M is controlled by two major dominant genes.

Failure of Phomopsis Phaseoli to Produce Mature Pycnidia in Senescent Soybean Stems at the End of the Growing Season

Phomopsis phaseoli (Desm.) Sacc. [syn. P. sojae Lehman; teleomorph = Diaporthe pha? seolorum (Cke. & Ellis) Sacc] does not produce mature pycnidia in senescent or dead soybean stems at the end of the growing season. Conidia did not form in pycnidia on stems collected from the field from October through December and incubated in laboratory moist chambers. Conidia were found in pycnidia after incubation of stems collected in January but conidia were not released from pycnidia under laboratory conditions until the May collection. Max? imum production of conidia on overwintered stems occurred in mid-June and declined to zero by early August. Production and release of conidia were induced on dead, non-overwintered stems by culturing on different agar media, and were highest on water agar plus 1 g/1 of allantoin. Weathering of stems in the field is evidently required for maturation of pycnidia of P. phaseoli to occur, perhaps due to the liberation of nutrients from decomposing host tissue. This may be the first report of a weathering requirement for the maturation of fruiting bodies by an anamorphic fungus. Phomopsis phaseoli (Desm.) Sacc. (syn. P. sojae Lehman) (Kulik, 1984) [te? leomorph = Diaporthe phaseolorum (Cke. & Ellis) Sacc] causes pod and stem blight and seed decay of soybean [Glycine max (L.) Merr.]. In late spring, conidia are released from pycnidia borne on overwintered stems and other crop debris (Lehman, 1923). During the growing season, conidia are also liberated from pyc? nidia on infected plant parts of the current crop, such as fallen cotyledons and petioles (Lehman, 1923; Kmetz et al., 1979). Mature pycnidia with exuding co? nidia also form in abundance on P. phaseoli-infecXed stems collected during the summer and incubated in a moist chamber. At the end of the growing season, when plants are mature and bearing pods, numerous, immature, black pycnidia appear on infected stems (Lehman, 1923). Phomopsis phaseoli is seedborne and may be isolated readily from infected seeds at harvest or from storage. This fungus usually fruits abundantly on seeds cultured on agar or on seed germination blotters, often accompanied by copious conidial exudation. In an attempt to collect non-seedborne isolates of P. phaseoli during the late summer and early fall of 1977 and 1978, it was noticed that conidia would not be produced in nor exuded from pycnidia of this fungus on senescent soybean stems collected at the end of the growing season and placed in laboratory moist chambers. This was surprising because abundant, sporulating pycnidia invariably formed on stems collected during the summer and incubated in the same fashion. The present study was undertaken to determine whether this was an isolated phenomenon or part ofthe normal life cycle of P. phaseoli, at least at Beltsville. MATERIALS AND METHODS To minimize any effects of cultivars or soil differences, the soybean stems used in this study were taken at random as needed from non-harvested plots of 51

Failure of Phomopsis phaseoli to Produce Mature Pycnidia in Senescent Soybean Stems at the End of the Growing Season

Phomopsis phaseoli (Desm.) Sacc. [syn. P. sojae Lehman; teleomorph = Diaporthe phaseolorum (Cke. & Ellis) Sacc.] does not produce mature pycnidia in senescent or dead soybean stems at the end of the growing season. Conidia did not form in pycnidia on stems collected from the field from October through December and incubated in laboratory moist chambers. Conidia were found in pycnidia after incubation of stems collected in January but conidia were not released from pycnidia under laboratory conditions until the May collection. Maximum production of conidia on overwintered stems occurred in mid-June and declined to zero by early August. Production and release of conidia were induced on dead, non-overwintered stems by culturing on different agar media, and were highest on water agar plus 1 g/1 of allantoin. Weathering of stems in the field is evidently required for maturation of pycnidia of P. phaseoli to occur, perhaps due to the liberation of nutrients from decomposing host tissue. This may be the first report of a weathering requirement for the maturation of fruiting bodies by an anamorphic fungus.

Symptomless Infection, Persistence, and Production of Pycnidia in Host and Non-Host Plants by Phomopsis batatae, Phomopsis phaseoli, and Phomopsis sojae, and the Taxonomic Implications

Phomopsis batatae, P. phaseoli, and P. sojae were able to infect, without production of obvious symptoms, seedlings of sweet potato and of 16 legumes inoculated in the greenhouse. These fungi produced pycnidia on inoculated seedlings incubated in laboratory moist chambers. Under conditions of natural infection in the field, P. sojae was recovered from stems of 14 of 21 legumes. This fungus was also isolated from seeds of cowpea and lima bean as well as from soybean, its usual host. The interpretation of these results questions the validity of regarding these anamorphs as three distinct species. Taken with the close similarity in morphology reported for these taxa in the literature and observed in my own isolates and in herbarium specimens, I conclude that these taxa are all one species, the valid name of which is Phomopsis phaseoli (Desm.) Sacc. For similar reasons, I consider the teleomorphs Diaporthe phaseolorum var. batatatis, var. phaseolorum, and var. sojae to be one and the same taxon, D. phaseolorum (Cooke & Ellis) Sacc. I believe that teleomorphic and anamorphic isolates from stem cankers and blighted tops of soybean should be provisionally called D. phaseolorum f. sp. caulivora and P. phaseoli f. sp. caulivora, respectively, until it can be demonstrated by a non-wounding technique that they can cause these pathological conditions when re-introduced into the host.

The Development of Diaporthe phaseolorum Variety Sojae in Culture

The development of the Phomopsis state of Diaporthephaseolorum var. sojae is described briefly. Both a and J conidia are produced from similar phialides. The isolate studied is homothallic but has trichogynes or trichogyne-like hyphae in early developmental stages. Perithecia develop from initials that include an ascogonial coil surrounded by enveloping hyphae. Perithecial initials ultimately differentiate into an outer peridium, a prominent centrum pseudoparenchyma layer, and paraphyses. Peridial and centrum hyphae in the apical region proliferate early in development to produce an elongate, periphysis-lined neck. The ascogenous system develops from the terminal portion of the ascogonial coil by septation of coil cells and subsequent production of short, ascogenous hyphae. The ascogenous hyphae proliferate to form a hemispherical basal hymenium. Asci are produced from croziers. The asci become detached from the hymenium and fill the centrum, compressing paraphyses and pseudoparenchyma. Development of D. phaseolorum var. sojae is believed to be a variation of the basic developmental pattern known in some other Pyrenomycetes. Data obtained from developmental studies of perithecia play an important role in current systematic concepts of pyrenomycetous fungi. The major source of this emphasis comes from Luttrell's comprehensive review (26) of perithecial development where developmental patterns were conceived as centrum types characteristic of various taxonomic groups. The present study is the third in a series of investigations of perithecial development in representative Pyrenomycetes. Previous studies on Hypoxylon serpens (Pers. : Fr.) Kickx (17) and Gelasinospora reticulospora (Greis & Greis-Dengler) Moreau & Moreau (18) revealed that perithecial development in these fungi could be viewed as a variation on the same basic ontogenetic pattern. Nonetheless, these two fungi belong to different families and represent the Xylaria and Sordaria perithecial centrum types, respectively. An additional centrum type believed to represent the Diaporthales has received little detailed study. The Diaporthe type centrum has traditionally been depicted as lacking paraphyses in the perithecium, although Luttrell himself has questioned the universality of this concept (27). More recently, studies in the genus Gnomonia by Fayret and Parguey-Leduc (10) and Huang and Luttrell (16) have provided evidence that paraphyses exist in fungi that are unquestionably members of the Diaporthales. There have been, however, no comprehensive developmental studies on Diaporthe, the type genus of the Diaporthales. The present study was therefore undertaken.

The Development ofDiaporthe PhaseolorumVarietySojaein Culture

The Development of<i>Diaporthe Phaseolorum</i>Variety<i>Sojae</i>in Culture

Mycoflora of soybean leaves, pods, and seeds in Mississippi

Fifty-six fungal taxa, 10 of which were previously unreported from soybean, were isolated from soybean leaves, pods, or seeds periodically sampled during two growing seasons. Incidence of fungi varied annually owing in part to differences in rainfall. Some of the more frequently isolated fungi, in order of prevalence, were Alternaria alternata, Diaporthe phaseolorum var. sojae, and Phorna spp. (from leaves); D. phaseolorum var. sojae, A. alternata, and Fusarium spp. (from pods); and Fusarium spp., D. phaseolorum var. sojae, and A. alternata (from seeds). Frequency of occurrence of the more prevalent fungi usually increased in plant tissues throughout the sampling period while other fungi often decreased in frequency. Incidence of some fungi was related to the spatial distribution of plant organs from which they were isolated.

Potassium Fertilization Effects on Phomopsis Seed Infection, Seed Quality, and Yield of Soybeans1

AbstractSoybeans [Glycine max (L.) Merr.] are often damaged by the seedborne fungi Phomopsis sp. and Diaporthe phaseolorum (Cke. and Ell.) Sacc. in regions where the climate is warm and humid during and after maturation. Incidence of these fungi is sometimes decreased by soil application of K fertilizer to improve crop growth. This study was designed to determine if high levels of soil available K, or K fertilizer applications beyond that necessary to maximize yield, would have a significant effect on seed‐borne fungi and seed quality.Soybeans were grown on Granby loamy fine sand (sandy, mixed, mesic Typic Haplaquoll), on Canfield silt loam (fine‐loamy, mixed, mesic Aquic Fragiudalf), and on Crosby silt loam (fine, mixed, mesic Aerie Ochraqualf). Potassium fertilizer was applied at various rates to establish a range of available K in soil. Potassium concentration of leaves closely paralleled K fertilizer treatments and the soil K levels. Seed was harvested from mature plants, and seed‐borne fungi were identified on samples cultured on potato‐dextrose agar. Phomopsis sp. was the most common fungus isolated from soybeans, ranging up to a 63% incidence. Diaporthe phaseolorum occurred with much less frequency, rarely exceeding a 10% incidence.Potassium fertilization nearly always decreased moldy seed, but increased seed germination and yield somewhat less frequently. Where germination was increased by K fertilization, the incidence of Phomopsis sp. and D. phaseolorum nearly always remained unchanged. Thus, K fertilization usually does not influence Phomopsis sp. and D. phaseolorum infection of seed, but possibly limits fungal growth after infection has occurred. Fertilizer rates in excess of that necessary to maximize yield had little influence on germination or moldy seed.Occurrence of Phomopsis sp. was greater in seeds from lower nodes than from upper nodes; whereas, the reverse was true of D. phaseolorum. Even though K deficiency symptoms occurred only on upper fruits and leaves, K fertilization decreased Phomopsis sp. 23 percentage points in lower seeds in contrast to 14 percentage points in upper seeds. Infection of seed by Phomopsis sp. within a plant does not appear to be related to K deficiency symptoms.

Seed‐borne Fungi, Quality, and Yield of Soybeans Treated with Benomyl Fungicide by Various Application Methods1

AbstractSoybeans [Glycine max (L.) Merr.] are often damaged by the seedborne fungi Phomopsis sp., Diaporthe phaseolorum (Cke. and Ell.) Sacc. var. sojae (Lehman) Wehm. and D. phaseolorum var. caulivora Athow and Caldwell which inhibit germination and sometimes cause moldy seed. These fungi can be controlled with benomyl (methyl 1‐[(butylamino)carbonyl]‐1H‐benzimidazol‐2‐ylcarbamate) fungicide when applied at the R4‐R5 stage in relatively large, illegal, quantities, &gt;1.1 kg/ha (a.i.), and in large volumes of spray solution, &gt;230 liters/ha. The purpose of this research was to determine if Phomopsis and Diaporthe seed contamination and seed rot can be effectively controlled with legal rates of benomyl applied by aircraft or ground equipment at reduced volumes.Aircraft application of benomyl at 0.56 kg/ha resulted in no overall improvement in seed germination, and on only 4 of 14 farms were there significant reductions in Phomopsis and Diaporthe seed contamination following benomyl application, but these were not large enough to be economical.Ground application was with a backpack mistblower, a tractor‐mounted Myers Downdraft sprayer, a high‐clearance powered unit using hydraulic broadcast application with flat‐fan nozzles, and the high‐clearance unit with a special boom using a directed hydraulic spray.Phomopsis + Diaporthe seed contamination in the controls ranged from 34 to 94% and germination, 10 to 71%. Benomyl decreased Phomopsis + Diaporthe seed contamination 20 to 67% and increased germination 16 to 61%. Incidence of these fungi in seed decreased and germination percentage increased with increasing spray volume where hydraulic flat‐fan nozzles were used, but not with the other methods. With equal volumes (230 liters/ha) the mistblower and downdraft sprayer were superior to the hydraulic flat‐fan broadcast method, and equal to a directed hydraulic spray for controlling Phomopsis and Diaporthe. Improvement in germination was sufficient to warrant application of benomyl with ground equipment.

Factors affecting sporulation by Phomopsis phaeolorum

Light and nutrition are the important factors in the production of pycnidia and conidia by cowpea isolates of the Phomopsis state of Diaporthe phaseolorum. The highest number of pycnidia and conidia were produced on plant tissue exposed to cool-white fluorescent light. In semisynthetic media more pycnidia were formed at high glucose concentrations, but they matured more slowly than those formed at lower glucose concentrations. Both the level of conidiation and the percentage of pycnidia that formed conidia were higher at lower glucose concentrations. The best artificial medium for inducing a high number of pycnidia containing abundant conidia was one that contained 0.4% glucose and 0.4% NaNO3. A number of carbon sources could replace glucose in this medium.

Soybean Seed Decay: Prevalence of Infection and Symptom Expression Caused by Phomopsis sp., Diaporthe phaseolorum var. sojae, and D. phaseolorum var. caulivora

Soybean Seed Decay: Prevalence of Infection and Symptom Expression Caused by Phomopsis sp., Diaporthe phaseolorum var. sojae, and D. phaseolorum var. caulivora

Studies of seed-borne fungi of tropical pasture legume species

Fungi associated with seed of 22 tropical and three temperate pasture legume species were investigated and 42 species were isolated. Most species were obtained by using the blotter method, which required supplementing with procedures such as isolation onto potato dextrose agar and Nash–Snyder agar to ensure the isolation of as many species as possible from each seed sample. In order to isolate storage fungi, seeds were incubated on salt–malt agar. This medium was also effective in isolating pathogens which survived for long periods in seed, which suggests that such pathogens may share with storage fungi physiological characteristics which aid survival in seed. Eight species – Fusarium acuminatum, F. avenaceum, F. equiseti, F. fusarioides, F. oxysporum, F. poae, Diaporthe phaseolorum and Phoma sorghina – were proven pathogenic to a range of hosts, while four others – Botrytis cinerea, Cladosporium cladosporioides, Myrothecium leucotricha and an unidentified species of Fusarium – are regarded as possibly pathogenic and worth investigating. All species of Fusarium generally reduced emergence and root growth more than shoot growth although F. oxysporum reduced shoot growth more than emergence or root growth. F. equiseti was the most severe pathogen among the Fusaria and was also very common in seed samples. D. phaseolorum, not previously reported on Macroptilium, Stylosanthes or other leguminous hosts in Australia, caused serious damage to flowers and young pods, and seriously reduced seed set and altered the proportions of hard and soft seed in more mature infected pods. In infected pods most soft seed became infected and few infected seeds germinated. D. phaseolorum was isolated only from freshly collected seed, where it was present in embryo and cotyledonary tissue. P. sorghina caused leaf spotting and pod blight. Leaf infection caused reduction in root growth and a corresponding reduction in nodulation. Pod infections reduced seed set and produced a high proportion of infected seed. Infected seed generally failed to germinate. P. sorghina was also found in embryo and cotyledonary tissue and survived in infected seed for at least 5 years. One storage fungus, Aspergillus ruber, was a seed (embryo) pathogen. In freshly infected seed, germination resulted in abnormal seedlings. Seed infected for several months failed to germinate. Hard seed were generally free of storage and pathogenic fungi, while soft seed were commonly infected. Abnormal and damaged seed were the most likely to carry pathogens and other fungi.

Mycotoxicosis in Chicks Produced by Toxins from Phomopsis sp. or Diaporthe phaseolorum var. sojae

The possibility of producing toxic effects in day-old chicks with mycotoxins from Phomopsis sp. or Diaporthe phaseolorum var. sojae isolates was studied. Evidence was found that Phomopsis sp., but not Diaporthe, produces hepatic necrosis with high mortality in chicks. Enzymatically, the hepatotoxin produced by Phomopsis sp. caused an increase in the level of liver glucose-6-P dehydrogenase. Mycotoxicosis caused by Phomopsis sp. was compared with lupinosis.

Pod Protection Effects on Soybean Seed Germination and Infection with Diaporthe phaseolorum var. sojae and other Microorganisms

Pod Protection Effects on Soybean Seed Germination and Infection with Diaporthe phaseolorum var. sojae and other Microorganisms