bimari gahii
Description:
Two major wilt diseases of tomatoes are Fusarium and Verticillium wilt. Fusarium wilt, the most prevalent of the two diseases, in Kansas generally occurs in midsummer when air and soil temperatures are high. Diseased plants first develop a yellowing of the oldest leaves (those nearing the ground). Often the yellowing is restricted to one side of the plant or even to leaflets on one side of the petiole. The affected leaves soon wilt and dry up, but they remain attached to the plant. The wilting continues on successively younger foliage and eventually results in the death of the plant. The stem remains firm and green on the outside but exhibits a narrow band of brown discoloration in the vascular tissue. This discoloration can be viewed easily by slicing vertically through the stem near the soil line and looking for a narrow column of browning between the central pith region and the outer portion of the stem.
Verticillium wilt tends to develop during the cooler periods of late spring. Symptoms of this disease are similar to Fusarium wilt. Older leaves are affected first; they turn yellow, wilt and eventually drop from the plant. Unlike Fusarium wilt, Verticillium wilt causes uniform yellowing and wilting of the lower leaves. As the disease progresses, younger leaves begin to wilt and die, until only a few healthy leaves remain at the top of the plant. Although diseased plants are not killed, they are stunted and weak and produce small fruit. Verticillium wilt also causes discoloration of the vascular system almost identical to that in Fusarium wilt except that the browning does not extend quite as far up the stem. Thus, laboratory analysis may be required to distinguish between the two diseases.
Life Cycle:
The Fusarium wilt fungus can be introduced into fields on contaminated seed or in infected transplants. Once introduced, the fungus can survive for many years in the soil. The Verticillium wilt fungus also is a soil-borne pathogen that can attack a wide range of plants, including potato, eggplant, strawberry, black raspberry, and many common weeds. Both fungi invade the plant through the fibrous root system and disrupt water and mineral uptake within the plant. Infection and disease development in Fusarium wilt are favored by warm soil temperatures (80° F) and low soil moisture, while Verticillium wilt develops best at relatively cool (55-75 F) soil temperatures.
Recommendations:
Long rotations (4-6 years) may help to reduce fungal inoculum levels in the soil, but it will not completely control these diseases. The most practical means of controlling Fusarium and Verticillium wilt is the use of resistant varieties. Many of the popular varieties of tomatoes have resistance to the common race (race 1) of the Fusarium fungus, to the Verticillium fungus, or to both. A few tomato varieties with resistance to Verticillium (V) and/or Fusarium (F) include: Early Cascade (VF); Celebrity (VFN); Avalanche (F); Jet Star (VF); Show me (VF); Burpee’s (VF); and Beefmaster (VFN). Information on varieties with resistance may be obtained from seed catalogues.
|
Tomato Diseases Worldwide, more prevalent in warmer climates |
|
|
|
|
| |||||
|
Damage Symptoms Yellowing of the foliage, beginning with the lower leaves and working upward. Yellowing often begins on one side of the vine. Infected leaves later turn brown. The top of the vine wilts during the day and recovers at night. Wilting becomes progressively worse until vines are permanently wilted. Vascular browning extends far up the stem and into large petioles. |
|
| |||||
|
|
|
|
|
Control |
|
|
SYMPTOMS
The Fusarium wilt fungus infects plants through the rootlets, invading the xylem and eventually extending throughout the plant. Individual branches and associated leaves on plants infected with Fusarium become yellow and wilt. Sometimes only one branch or one side of the plant is affected, creating a yellow flag effect. Infected plants usually die. A dark brown vascular discoloration extends far up the stem. Symptoms often first appear during fruit sizing.
COMMENTS ON THE DISEASE
Symptoms of Fusarium and Verticillium wilts are similar and may require culturing the fungus in a laboratory for positive identification. Fusarium wilt can greatly reduce yields in fields with a high incidence of Fusarium. The fungus overwinters and survives for many years in the soil as spores. Long distance spread is by seed, transplants, and soil on farm machinery. The disease is favored by warm weather. The fungus only infects tomato but exists as three races. Race 1 is widespread; Race 2 is common in the Sacramento Valley and in the northern San Joaquin Valley; and Race 3 is in the Sacramento Valley and spreading into the San Joaquin Valley.
MANAGEMENT
Use resistant tomato varieties. Resistant varieties are common for Race 1, and many are also resistant to Race 2. A few varieties are resistant to all three races. Limit the spread of infested soil by cleaning farm equipment. Avoid root knot nematode infestations because nematode feeding can overcome the plant resistance to Fusarium wilt. Rotation out of tomatoes for several years reduces inoculum level, although Fusarium is long-lived.
از خدا خواستن عزت است اگر برآورده شود رحمت است و اگر نشود حكمت است. از خلق خدا خواستن خفت است اگر برآورده شود منت است اگر نشود ذلت است