Question

Apple scab is caused by
A. Puccinia
B. Erysiphe
C. Ustilago
D. Venturia

Answer 1

It is a fungus that grow on non-living and living things. This fungus has several host-specific strains that can cause disease on one type of plant but not any other.

Complete step by step answer: a. Puccinia - The black stem and cereal rusts are caused by the fungus Puccinia graminis. They are one of the significant disease-causing organisms in cereal crops. Crops that are affected by this fungus are bread wheat, durum wheat, triticale and barley.
b. Erysiphe - This is a plant pathogen that belongs to the family of Erysiphaceae. It causes powdery mildew of crucifers on Brassica family plants like cauliflower, cabbage, Brussels and broccoli.
c. Ustilago - This belongs to the family Ustilagineous with approximately 300 species and most species are parasites that affect monocotyledonous plants.
d. Venturia - This causes a serious disease to apples and ornamental crab-apples. Venturia inaequalis attack both fruits and the leaves. The fungal disease forms olive green to pale yellow spots on the upper surface of the leaf. Velvety dark spots appear on the lower side of the leaf. The infected leaves become twisted and puckered and may drop off early from the plant.
Hence, the correct answer is option D.

Note:Venturia inaequalis fungus belongs to the family of ascomycetes and they cause severe disease in the malus trees such as apple tree. Symptoms that are found on the leaf will be the same on the fruits. Scabby spots are sunken and tan and have a velvety like texture in the centre of the spore. As these spots mature, they spread and turn brownish and corky. The fruits which have been infected by this becomes distorted and many cracks allowing entry of secondary organisms. The fruits that are infected may fall earlier from the tree.