User:Blouisje/sandbox

DEFINTION: Black Point is a fungal disease that occurs in wheat. It is the occurrence of a dark discoloration that is present at the embryo end of the grain. It can occur at any time from grain filling to near harvest. In black point the tip of the embryo shows a black to brown discoloration that extends into the crease of the kernel. This discoloration that is present at the embryo end of the grain is the cause of substantial financial losses to wheat growers. Evidence suggest that fungal infection is the main correlation to the symptoms of Black Point. This disease is favored by weather that is warm and humid at grain filling near maturity. The primary fungi that is associated with black point are known to be Alternaria spp., Cochliobolus sativuis as well as Cladosporium spp. These fungi do not produce toxins, but C. sativuis is known for reducing germination. Although it is usually not yield-reducing, the presence of black point in harvested grain can reduce grade and quality,resulting in dockage by the elevator. Affected kernels are considered by U.S. grain standards to be damaged and only 2 percent are permitted in wheat graded as U.S. No. 1 and 4 percent in U.S. No. 2. The problem that comes with black point problem of wheat develops during the ripening process of the grain. Fungi enters the senescing glumes, floral parts, and the brush hair of the ripening seed during moist, warm weather. Spores are produced, which then penetrate both glumes and testa of the seed (Harvey 1985). If moist, warm weather continues the grain may blacken evenly. If the rainy period is followed by dry weather, black bands appear on the grain as fungal growth stops. The black discoloration is found most often in the germ region extending into the crease of the kernel. DISEASE IMPACT: With black point there is an associated disease impact that comes with it as well as a reduction of several factors. There is a reduction of test weight, market grade and dockage by the elevator and there is also reduced germination or increased incidence of seedling blight (associated with C. sativius not with Alternaria or Cladosporium species. SYMPTOMS: The pericarps of maturing wheat kernels turn dark brown to black, with the discoloration usually restructed to the germ-end of the kernel (33; 34 is healthy seed). If caused by Alternaria spp., the dark color affects only the pericarp; if caused by Helminthosporium or Fusarium spp., the germ may be invaded and injured or killed. There are other fungi that can cause black point, but the three noted here are the most common. MANAGEMENTS Usually at the embryo (germ end) kernels are noticed to be discolored or blackened. The entire kernel, or just a portion of it, can be discolored. Although most often not yield-reducing, black point can have the affect to reduce grade and quality. According to U.S. wheat standards, kernels that are blackened are in fact considered to be damaged, and only 2% are permitted in wheat graded as US No.1, and 4% in US No.2. Black point is especially important on durum wheat because black specks can appear in the semolina, making it undesirable for further processing. Black point can be partially controlled by reducing irrigation frequency after heading and by reducing nitrogen rates, without sacrificing either yield or quality. Because black point can occur at damaging levels in some seasons despite modifications in cultural practices, the best option for control is to combine reduced input practices with black point resistant cultivars. Current cultivars differ in the level of resistance or tolerance to the disease, although there are no completely resistant cultivars available. This disease is of minor importance. Only when the disease percentage is high, it causes concern to the trader and the consumer. The discolored seeds are mostly shrivelled and they are separated out during processing. The black point disease is very difficult to control. Because the fungi that cause it are readily air-borne, cultural practices are of little, if any, value. The most promising method of control is the development of more resistant varieties. Most varieties grown in New Zealand show adequate resistance. Takahe and Kopara are the most susceptible cultivars.

Development: Usually, kernels are infected by these fungi during the dough stage. If humid weather prevails for a few days to a week just prior to harvest, the incidence of infection will increase and black point will develop in many cultivars. Disease causes blackening of embryonic region of the seed (black point), discoloration of area beyond the embryonic region (black discoloration (Caused by Aalternata, Curvularia lunate, Epicoccum sp., Bipolaris sorokiniana, etc.) and eye-spot symptom (B. sorokiniana). The warm and humid weather at grain filling or near maturity favors this disease.

Hosts/Distribution: Wheat is the principal host; triticale and several related grasses also can be affected. Distribution is worldwide, wherever small grain cereals are grown.

Importance: Losses are due mainly to discounted prices paid for discolored grain; if Fusarium or Helminthosporium spp. are involved, the viability of the seed also may be reduced. focus on black point in other species