| Diaporthe phaseolorum var. caulivora | |
|---|---|
Scientific classification  | |
| Kingdom: | Fungi |
| Division: | Ascomycota |
| Class: | Sordariomycetes |
| Order: | Diaporthales |
| Family: | Diaporthaceae |
| Genus: | Diaporthe |
| Species: | |
| Variety: | D. p. var. caulivora |
| Trinomial name | |
| Diaporthe phaseolorum var. caulivora Athow & Caldwell | |
| Synonyms | |
Diaporthe phaseolorum f.sp. caulivora Contents | |
Diaporthe phaseolorum var. caulivora is a fungal plant pathogen which infects soybean, causing soybean stem canker. [1]
Soybean (Glycine max) is the most economically important host of soybean stem canker caused by Diaporthe phaseolorum var. caulivora. Since the early 1940s, Stem Canker was a prevalent disease in the upper Midwest. [2] Soybean host plant susceptibility has been researched since the early 1950s, bringing light to the need for developing resistant varieties. [3] Botanist AA Hildebrand [3] ran a varietal selection experiment to determine susceptible varieties in northern climates. Successful removal of susceptible cultivars “Hawkeye” and “Blackhawk” greatly reduced the impact of this disease. [2] In the past 30 years, successful breeding for resistant varieties has greatly reduced the significance of this disease in certain parts of the country, however sporadic incidences of the disease still occur. [4] In soybean, the main factor affecting disease susceptibility is the presence or absence of resistance genes in specific cultivars. [4]
Along with soybean, many common weed species have been studied as potential hosts. Investigations have identified 13 weed species for soybean stem canker when inoculated directly with ascospores. [5] Inoculation success to these weeds species was found in greenhouse experiments though outdoor trials were not as successful. More recently, many weed species, such as black nightshade, curly dock, and morning glory, have been confirmed as susceptible hosts, yet few show symptomology of the disease until plant death. [6] Weed species as host for this disease are of particular interest because of their potential to act as an inoculum for the disease on soybean.
Disease symptoms occur primarily on the stems, leaves and can lead to whole plant symptoms. [2] Reddish brown lesions on the lower stem of soybean plants progress into brown cankers. In some cases, the disease can spread to all parts of the stem. Stem girdling can result in premature plant death. [2] Grey streaking along the lower stem and taproot has also been observed. Studies suggest a toxin may influence the development and symptomology of stem canker. [7] Leaf symptoms include interveinal chlorosis and necrosis during early reproductive stages. Leaves eventually dry and fall off the plant as the disease worsens. [4] Stem canker has similar symptomology as brown stem rot, fusarium wilt, phytopthora stem rot, sudden death syndrome, tobacco streak virus, and sclerotinia stem rot, which can make distinguishing this disease particularly difficult. [6] Stem canker can be differentiated primarily by its long dark red or brown canker that can extend over multiple nodes. Inside the stem, discoloration is localized to areas near the canker or lesion. [6]
Environmental conditions during the vegetative growth stage are most important for stem canker development. [8] When plants are infected at V3 growth stage they are subject to the highest severity of disease of any growth stage. The combination of early growth stage susceptibility to disease and optimal environmental conditions can cause a stem canker epidemic if not treated properly. Fields subjected to hail damage have been shown to have increased stem canker severity. [9]
The optimal air temperature for infection occurs at 83.5 °F, [8] while infection readily occurs when temperatures are between 82 °F and 93 °F. Along with optimal temperature, moisture is needed for infection. During vegetative growth stages, rainfall is crucial to the development of stem canker infections. Cumulative rainfall is positively related to higher disease severity. [8] Further, if dry conditions follow wet conditions during vegetative growth stages, plant mortality increases. [8] This is because the disease inhibits the flow of water through the stem to plant extremities, therefore dry periods after infection stress plants more than wet periods after infection. [10]
Management of soybean stem canker is greatly influenced by proper cultivar selection. Selecting resistant soybean varieties is currently the best management practice for this disease, followed by crop rotation to a non-host crop. [6] Furthermore, soybean grown for seed should not be planted if harvested from a field with a history of stem canker. [8] In-furrow fungicides applied at planting can reduce infestation to seed during germination, but will not control the disease completely. [8] Rotations in to corn, wheat or sorghum for at least 2 years is recommend after a severe infestation. [6]
Fungicide sprays for this disease may not be effective on susceptible cultivars, however will manage an outbreak in moderately susceptible cultivars. Fungicides, such as benzimidazoles, should be sprayed during the early vegetative growth stages to avoid an outbreak. Minimum or no till fields have a higher susceptibility to stem canker because of the increased amount of crop residue that increases the survival rate of the disease. Incorporation of residue or tillage will reduce disease development in the field. Lastly, high organic matter and/or high fertility levels can positively influence stem canker infestation. To manage this, use best management practices to maintain sufficient soil fertility levels. [6]
Rusts are plant diseases caused by pathogenic fungi of the order Pucciniales.
Phytophthora sojae is an oomycete and a soil-borne plant pathogen that causes stem and root rot of soybean. This is a prevalent disease in most soybean growing regions, and a major cause of crop loss. In wet conditions the pathogen produces zoospores that move in water and are attracted to soybean roots. Zoospores can attach to roots, germinate, and infect the plant tissues. Diseased roots develop lesions that may spread up the stem and eventually kill the entire plant. Phytophthora sojae also produces oospores that can remain dormant in the soil over the winter, or longer, and germinate when conditions are favourable. Oospores may also be spread by animals or machinery.
Leptosphaeria maculans is a fungal pathogen of the phylum Ascomycota that is the causal agent of blackleg disease on Brassica crops. Its genome has been sequenced, and L. maculans is a well-studied model phytopathogenic fungus. Symptoms of blackleg generally include basal stem cankers, small grey lesions on leaves, and root rot. The major yield loss is due to stem canker. The fungus is dispersed by the wind as ascospores or rain splash in the case of the conidia. L. maculans grows best in wet conditions and a temperature range of 5–20 degrees Celsius. Rotation of crops, removal of stubble, application of fungicide, and crop resistance are all used to manage blackleg. The fungus is an important pathogen of Brassica napus (canola) crops.
Rhizoctonia solani is a plant pathogenic fungus with a wide host range and worldwide distribution. It was discovered more than 100 years ago. R. solani frequently exists as thread-like growth on plants or in culture, and is considered a soil-borne pathogen. R. solani is best known to cause various plant diseases such as collar rot, root rot, damping off, and wire stem. R. solani attacks its hosts when they are in their early stages of development, such as seeds and seedlings, which are typically found in the soil. The pathogen is known to cause serious plant losses by attacking primarily the roots and lower stems of plants. Although it has a wide range of hosts, its main targets are herbaceous plants. R. solani is a basidiomycete fungus but the teleomorph stage is not prominent. Occasionally, sexual spores (basidiospores) are produced on infected plants. The disease cycle of R. solani is important in management and control of the pathogen. The pathogen is not currently known to produce any asexual spores (conidia), though it is considered to have an asexual lifecycle perpetuated through sclerotia.
Alternaria alternata is a fungus which has been recorded causing leaf spot and other diseases on over 380 host species of plant. It is an opportunistic pathogen on numerous hosts causing leaf spots, rots and blights on many plant parts.
Phytophthora citrophthora, also known as brown rot of citrus, is a soil borne oomycete that infects several economically important citrus crops. A diagnostic symptom of P. citrophthora is gummosis, wherein lesions around the base of the tree exude sap. Other common symptoms include dark longitudinal lesions forming at the soil line, a sour smell, and eventual cracking of the bark. Advanced symptoms include yellowing and necrosis of the tree canopy. Girdling action caused by the pathogen around the trunk can often cause the collapse of the tree. Resistant lemon varieties have been developed and their implementation has been effective at controlling the spread of the disease. Fruits that have been infected with P. citrophthora exhibit symptoms of brown rot characterized by a distinct odor. This disease is most active in the moderate temperatures of spring, fall, and winter months, opposite of most other Phytophthora species.
Phanerochaete salmonicolor is a fungal plant pathogen which has become a serious problem, especially in Brazil. P. salmonicolor is a member of the Corticiaceae family, which is a paraphyletic group classified based on their basidiocarps. This pathogen causes Pink Disease, most commonly in citrus, although P. salmonicolor has a wide host range including rubber and cacao trees. Pink Disease causes branch and stem die-back due to canker formation. The cankers are recognizable by gum exudation and longitudinal splitting of the bark.
Puccinia schedonnardii is a basidiomycete fungus that affects cotton. More commonly known as a “rust,” this pathogen typically affects cotton leaves, which can decrease the quality of the boll at time of harvest. As large percentages of cotton in the United States are resistant to various rust varieties, there is little economic importance to this disease. In places where rust is prevalent, however, growers could see up to a 50% reduction in yield due to rust infection.
Pythium aphanidermatum is a soil borne plant pathogen. Pythium is a genus in the class Oomycetes, which are also known as water molds. Oomycetes are not true fungi, as their cell walls are made of cellulose instead of chitin, they are diploid in their vegetative state, and they contain coenocytic hyphae, called a protist. Also, they reproduce asexually with motile biflagelette zoospores that require water to move towards and infect a host. Sexually, they reproduce with structures called antheridia, oogonia, and oospores.
Sclerotinia sclerotiorum is a plant pathogenic fungus and can cause a disease called white mold if conditions are conducive. S. sclerotiorum can also be known as cottony rot, watery soft rot, stem rot, drop, crown rot and blossom blight. A key characteristic of this pathogen is its ability to produce black resting structures known as sclerotia and white fuzzy growths of mycelium on the plant it infects. These sclerotia give rise to a fruiting body in the spring that produces spores in a sac which is why fungi in this class are called sac fungi (Ascomycetes). This pathogen can occur on many continents and has a wide host range of plants. When S. sclerotiorum is onset in the field by favorable environmental conditions, losses can be great and control measures should be considered.
Diaporthe helianthi is a fungal pathogen that causes Phomopsis stem canker of sunflowers. In sunflowers, Phomopsis helianthi is the causative agent behind stem canker. Its primary symptom is the production of large canker lesions on the stems of sunflower plants. These lesions can eventually lead to lodging and plant death. This disease has been shown to be particularly devastating in southern and eastern regions of Europe, although it can also be found in the United States and Australia. While cultural control practices are the primary method of controlling for Stem Canker, there have been a few resistant cultivars developed in regions of Europe where the disease is most severe.
Ascochyta pisi is a fungal plant pathogen that causes ascochyta blight on pea, causing lesions of stems, leaves, and pods. These same symptoms can also be caused by Ascochyta pinodes, and the two fungi are not easily distinguishable.
Cercospora sojina is a fungal plant pathogen which causes frogeye leaf spot of soybeans. Frog eye leaf spot is a major disease on soybeans in the southern U.S. and has recently started to expand into the northern U.S. where soybeans are grown. The disease is also found in other soybean production areas of the world.
Diaporthe phaseolorum var. sojae is a plant pathogen infecting soybean and peanut.
Fusarium circinatum is a fungal plant pathogen that causes the serious disease pitch canker on pine trees and Douglas fir. The most common hosts of the pathogen include slash pine, loblolly pine, Monterey pine, Mexican weeping pine, and Douglas fir. Like other Fusarium species in the phylum Ascomycota, it is the asexual reproductive state of the fungus and has a teleomorph, Gibberella circinata.
Gummy Stem Blight is a cucurbit-rot disease caused by the fungal plant pathogen Didymella bryoniae . Gummy Stem Blight can affect a host at any stage of growth in its development and affects all parts of the host including leaves, stems and fruits. Symptoms generally consist of circular dark tan lesions that blight the leaf, water soaked leaves, stem cankers, and gummy brown ooze that exudes from cankers, giving it the name Gummy Stem Blight. Gummy Stem Blight reduces yields of edible cucurbits by devastating the vines and leaves and rotting the fruits. There are various methods to control Gummy Stem Blight, including use of treated seed, crop rotation, using preventative fungicides, eradication of diseased material, and deep plowing previous debris.
Stem rot is a disease caused by a fungus infection in the stem. Fungus that causes stem rot are in the Rhizoctonia, Fusarium or Pythium genera. Stem rot can readily infect crops that are in their vegetative or flowering stages. The disease can survive up to five years in the soil. Symptoms of stem rot includes staining of infected area, reduced crop yield and crop failure. The disease can be spread through the use of unfiltered water as well as unsterilized tools. Also leaving previous dead roots in soil can increase the risk of stem rot. Spores can also enter the plant through injured stem tissue on the plant including from insect attacks. The fungus impedes stem functions like transporting nutrients. It can cause water to leak through the lesions of stem tissue. Common infected crop plants are soybeans and potatoes. An issue with maintaining this disease is the lack of management by crop producers. Producers of soybeans tend to not manage for the disease because it is not normally yield limiting in a large area. Fungicides can be used to manage the disease as well as burning the crop after harvest or letting it decompose.
Sudden Death Syndrome (SDS), a disease in soybean plants, quickly spread across the southern United States in the 1970s, eventually reaching most agricultural areas of the US. SDS is caused by a Fusarium fungi, more specifically the soil-borne root pathogen Fusarium virguliforme, formerly known as Fusarium solani f. sp. glycines. Losses could exceed hundreds of millions of dollars in US soybean markets alone making it one of the most important diseases found in Soybeans across the US.
Stenocarpella maydis (Berk.) Sutton is a plant pathogenic fungus and causal organism of diplodia ear and stalk rot. Corn and canes are the only known hosts to date. No teleomorph of the fungus is known.