Mango (Mangifera indica L.) is considered the king of fruit among tropical and subtropical regions of the world. In Pakistan, mango is cultivated on an area of 167.5 thousands hectares with the average production of 1732 thousand tones [1] . Mango is vulnerable to various diseases and disorders at all the stages of its augmentation from the nursery to the fruiting plants; which are the cause of its low production [2] [3] . All plant parts of the mango viz. stem, branches, twigs, leaves, petioles, blossoms and fruits are attacked by a number of pathogens. Powdery mildew of mango was present in Indo-Pak sub-continent before 1874 [4] . In Pakistan, disease emerged as a major limiting factor of mango production and the higher input costs have increased the economic importance of the disease. At present, mango orchards are facing a crucial problem of powdery mildew, caused by a fungus Oidium mangiferae Bert., a biotrophic parasite which lives and develops on the host plant tissues. Heavy losses are caused by this disease varying from 10% - 25%. The spread of the disease mainly depends on the weather conditions which facilitate the disease to proliferate among the orchards [5] . The pathogen survives in old leaves at plant or on the ground during the unfavorable conditions; where at the conidia are produced which will cause infection on other leaves, blossoms and fruits. The disease is characterized by the symptoms of white superficial powdery mycelium on inflorescence, leaves and young fruits [6] . The pathogen primarily affects the inflorescence resulted in premature shedding of the flowers and the young fruit before achieving pea size [7] [8] . The disease symptoms appeared in February and March, and the pathogen attacked on flower scales flower heads, young leaves stalks and fruits [9] . The study of the epidemiology and perpetuation of mango powdery mildew [10] showed that the fungus causes maximum infection on the host plant at 26˚C and 100% relative humidity. However, the fungus may cause the disease at 15˚C to 32˚C and 15.5% to 100% relative humidity. The atmospheric temperature was found to be the most important factor responsible for the onset of disease and its epidemic development under natural conditions. It was also observed that the relative humidity ranging from (65% - 78%) and a range of minimum temperature from 11˚C - 14˚C to a maximum temperature (30˚C - 40˚C) were noted to be favorable for the onset of mango powdery mildew infection. Resistance to the mango powdery mildew has been investigated in several countries by the researchers but no resistance has been found so far among the mango varieties. All the commercial varieties were found to be susceptible to powdery mildew of mango depending on the climatic factors [11] . The evaluation of mango varieties showed no commercial variety to be resistant against the mango powdery mildew [12] . The screening of eleven mango varieties against the mango powdery mildew showed no variety to be resistant against the disease [13] . Hence, the present study was conducted to determine the cultivar susceptibility, disease severity index and disease incidence percentage and average produce of each variety against the powdery mildew infection.

The results with reference to the powdery mildew of mango on flowers indicated that almost all the varieties were susceptible to the powdery mildew and showed a varying degree of infection percentage (Table 1). There was no variety found to be resistant against the disease. The pathogen attacks primarily on the flowers. Maximum disease incidence was observed (33.33%, 26.66% and 26.66%, 26.66%) on Dusehri, Chaunsa Samar Bahisht, Malda and Ratole No.12 respectively and minimum disease incidence was (3.66% and 3.66%) noted on Almas and Sensation. Disease severity index showed maximum infection on Dusehri followed by Chaunsa Samar Bahisht, Ratole No.12, Fajri, Sindhri and Malda respectively.

Powdery mildew has become more common and important disease in most of the mango growing areas of the world [15] [16] . The causal organism of the disease is a fungus Oidium mangiferae Berthet. The telemorph stage of this organism is still unknown. The specific symptoms of the disease occurred on young tissues of the all parts of flowers, leaves and fruits. Acute blossom infection may cause complete damage to fruit, flower remains closed and drop from the inflorescence. Almost all the inflorescence showed a pattern of disease from tip to downward and reveals itself by the development of wefts of white mycelium on the infested parts [9] [16] . The results of the experiment showed that the almost all the varieties were susceptible to the disease. Keeping in view the disease

Averages followed by the same letter in severity index and yield of fruit column do not differ statistically from each other (P ≤ 0.05), SE = 0.72, 16.05. T = tolerant, S = susceptible, MS = moderately susceptible, HS = highly susceptible. ^*Average incidence (minimum incidence, maximum incidence).

incidence percentage, the varieties showed eight different infection levels. In the first group, Dusehri was present with the maximum infection (33.33%). In the second group, Chaunsa Samar Bahisht and Ratole No.12 were present with the infestation of (26.66%). The third group included Fajri and Sindhri showed the infection level (23.33%). Similarly, in the next one were Langra, Saroli, Zafaran, Malda late and Early gold with (16.66%) infection. The two varieties Shan e Mustafa and Mahmood Khan showed (13.33%) infestation followed by Totapari, Ghulab e Khas and Chaunsa white with (11.66%) infection of the disease. Besides these, Armughan, Shan e Ali, Anmol, Yakta, Neelam, Anwar Ratole and Chaunsa Black showed (6.66%) infestation of the disease. The minimum disease incidence percentage was observed (3.33%) in Sensation and Almas. The varieties in eight groups were statistically similar. No variety was resistant to disease yet most of them showed a significant level of tolerance against the disease. Sensation and Almas presented low incidence value and they could be considered as resistant to the disease. The results of the disease severity index showed that there were two groups (A, AB) in which means were not statistically different. Maximum disease severity index was observed on Dusehri, Ratole No.12, Fajri, Sindhri, Chaunsa Samar Bahisht and Malda. Some varieties showed lowest disease severity index were Shan e Ali, Shan e Mustafa, Chaunsa White, Sensation, Ghulab e Khas and Armughan. The average number of fruit per tree significantly differed among all the varieties in five dissimilar groups in which the means were similar statistically ranging from 196 fruits (Almas) to 92 fruits (Armughan). The average (maximum) temperature during this experiment before the estimation of powdery mildew infection lingered around 25.6˚C to 31.2˚C whereas minimum temperature was recorded 11.2˚C to 20.0˚C. Precipitation was scarce during the assessment of disease while the last rainfall of 3.1 mm was recorded before the thirteen days of disease evaluation. On the whole, the atmospheric conditions were completely in favour of the disease by the fungus during the experiment as observed by [10] . Although some varieties showed a higher degree of powdery mildew infection yet, had a considerable yield; they could be considered as tolerant varieties. Rather the disease incidence was very high yet the fruit drop was not significant and a good yield was attained. The study provides useful information about the powdery mildew infection in mango orchards and served as a guide for future field experiments.

The various mango cultivars showed varying response in relation to the infection of powdery mildew. There was no variety found to be resistant against the disease although they attained significant yield. It might be concluded that the presence or absence of symptoms caused by the powdery mildew had no such effect on the fruit yield of the mango cultivars.

Grateful acknowledgements are to Mr. Muhammad Tariq Malik, Assistant Plant Pathologist at Mango Research Institute, Multan, and the owners of Bhatti Mango Farm for facilitating us to conduct this work.