Sunflower Crop DiseasesA Presentation To IPM Course/FFS Participants

ByMr. Allah Dad Khan

Provincial Coordinator IPM KPK For MINFAL Pakistan

Diseases

Sclerotinia head rot damaged fieldAt least 30 diseases, caused by various fungi, bacteria and viruses, have been identified on wild or cultivated sunflower, but only a few are of economic significance as far as causing yield losses. This section identifies many of the diseases affecting sunflower crops and provides information about the disease, its impact, and control measures.

Apical Chlorosis

Identification and Life Cycle • Apical chlorosis is caused by the

bacterium Pseudomonas syringae pv. tagetis. Although infected plants are conspicuous in the field, the disease is of little economic importance. The disease is most severe on seedlings during cold, wet weather. The pathogen can be disseminated among plants by splashing rain and irrigation water, by wind as aerosols, and by the movement of contaminated soil. The apical chlorosis pathogen is a very common resident on the leaves of many weeds and other crop plants, but also survives in the soi

Cultures of Pseudomonas syringae

Bacterial Leaf Spot

• Disease by P. syringae tends to be favoured by wet, cool conditions—optimum temperatures for disease tend to be around 12–25 °C, although this can vary according to the pathovar involved. The bacteria tend to be seed-borne, and are dispersed between plants by rain splash

• Symptoms

Bacterial Wilt

Symptoms • Septoria blight causes numerous small

( about 1/8" to 1/4" in diameter) brown spots that develop light tan to white center as they age. The overall effect of both blights is similar. Leaves turn yellow, brown, then wither and die. Septoria blight and early blight both overwinter on infected debris from previous years. If there are only a few plants in a garden, the progress of the blights may be slowed somewhat by removing infected leaves as they appear.

Crown Gall

Symptoms• Crown gall is caused

by Agrobacterium tumefaciens, a Gram-negative, bacilliform bacterium that is normally associated with the roots of many different plants in the field. This bacterium can survive in the free-living state in many soils with good aeration such as sandy loams where crown gall diseased plants have grown. The bacterium can also survive on the surface of roots (rhizoplane) of many orchard weeds.

Alternaria Leaf Blight

Downy Mildew

Damage: • Seedling infection seldom exceeds

25 percent of the field, although there have been exceptions. The infected plants die off very early and do not compete for nutrients with neighboring plants. If the infection is sporadic throughout the field, the compensating ability of sunflower will compensate and the yield impact will be minimal. However, if all or a majority of the plants in a part of the field are infected then the damage will be significant.

Powdery Midew

Rust

Septoria Leaf Spot Identification and Life Cycle

• Septoria leaf spot is caused by the fungus Septoria helianthi. Little is known about the survival and dissemination, but the disease cycle is thought to begin when spores (conidia) are deposited onto leaves by wind and/or splashing water. The fungus directly penetrates host tissues, and develops fruiting structures (pycnidia) that produce more conidia. The disease develops most rapidly during moderate to warm weather with abundant rainfall, especially after flowering. The fungus can be seedborne, and is thought to survive between sunflower crops in and on infected crop debris.

Pin Nematodes

Symptoms • Pin nematodes rarely cause damage to plants

unless present in very high numbers. However, mint is one of the best hosts for pin nematodes, and populations frequently exceed 100,000/quart soil. Effects of feeding by pin nematodes on the appearance, structure or function of mint roots has not been studied. In other crop plants, symptoms range from no noticeable pathology at the feeding sites to shallow localized lesions. Rate of root growth and lateral root development may be reduced or terminated by the prolonged feeding of many individuals on the same root. This may reduce the nutrients, and thus energy, which can be stored into the rhizome, potentially reducing the health and vigor of the plants.

Lesion Nematodes

Symptoms• Symptoms of lesion nematode

disease (as with most nematode-induced diseases) often go unrecognized initially because the nematodes (Figure 1) are microscopic pathogens of belowground plant parts (mainly roots), and the aboveground symptoms are often general symptoms of plant root stress. Low to moderate populations of lesion nematodes may cause no visible aboveground symptom

Lesion nematode inside root

Root Knot Nematodes

Symptoms• Root-knot nematode symptoms on plant

roots are dramatic. As a result of nematode feeding, large galls or "knots" can form throughout the root system of infected plants. Severe infections result in reduced yields on numerous crops and can also affect consumer acceptance of many plants, including vegetables (Figures 1, 2). The degree of root galling generally depends on three factors: nematode population density, Meloidogyne species and "race," and host plant species and even cultivar. As the density of nematodes increases in a particular field, the number of galls per plant also will increase

On carrot

Spiral Nematodes

Symptoms• The symptoms of Helicotylenchus

pseudorobustus are more subtle than those of certain other nematodes such as root-knot or sting nematodes. Heavy infection byHelicotylenchus pseudorobustus causes a reduction in the root system, leading to unthrifty plants. On turfgrasses, Helicotylenchus pseudorobustus has been shown to reduce root length and cause thinning of turf. Generally the turf decline will occur in patches

Stunt Nematodes

• Stunt nematodes damage the roots of field and vegetable crops. Once damaged, plants become exposed to many destructive soilborne microorganisms and pathogens. A major problem with determining the damage these nematodes cause is inadequate knowledge of their distinguishing characteristics, numbers, relationships and geographic distribution.

• Symptoms

Aster Yellow • Aster yellows is a virus-like disease caused by a

phytoplasma, an organism similar to a bacterium. The aster yellows phytoplasma is vectored by the aster leafhopper, an olivegreen or straw-colored leafhopper with six dark spots on its forehead. Aster leafhopppers migrate from the south, usually arriving in early to mid June. Serious outbreaks of aster yellows can be caused by large numbers of migrant leafhoppers in the spring, warm weather in May and June, and adequate precipitation and soil moisture. The aster leafhopper will not fly at temperatures below 60°F

• Symptoms

Sunflower Mosaic

Identification and Life Cycle • Sunflower mosaic can be caused by

three different viruses, namely Cucumber mosaic virus, Sunflower virus, and Tobacco mosaic virus. The most common virus causing sunflower mosaic is Cucumber mosaic virus. This virus can be mechanically- and aphidtransmitted and has a broad host range. Aphids can acquire and transmit Cucumber mosaic virus within 5 to 10 seconds of feeding. The virus can overwinter in many ornamental plants and weeds.

Chlorotic mottle

• Symptom development in a susceptible sunflower line inoculated with Sunflower chlorotic mottle virus (SuCMoV) was followed in the second pair of leaves at different post-inoculation times: before symptom expression (BS), at early (ES) and late (LS) symptom expression. Sugar and starch increases and photoinhibition were observed as early effects BS, and were maintained or enhanced later on, however, chlorophyll loss was detected only at LS. Photoinhibition correlated with a drastic decrease in D1 protein level

Other Diseases