Oidium mangiferae Berthet was found to be associated With the powdery mildew disease of mango. The air- borne conidia are released from the old tissue harboring the dormant fungal hyphae under favorable weather conditions, which produce the disease. Proper forecasting of release of airborne innoculum significantly reduced the required number of sprays needed for chemical control. Spore traps were used to monitor the concentration of airborne conidia during the months of February, March and April 1996 and l997. Daily temperature and relative humidity were noted and the spore counts from the spore traps were correlated to the meteorological data. There was a positive trend between rising temperature, lowering relative humidity and number of spores in the air alter a low temperature, high humidity and cloudy spell of weather. The maximum spore occurrences were noted around 25°C and relative humidity of 40-60%. It took 5-8 days for the emergence of disease symptoms after the first detection of airborne conidia. Ten fungicides were tested on three mango varieties (Langra, Dashehari, and Anwar Retol). The preventive sprays at the stage of first detection of air born conidia were effective in controlling the disease. Optimal timing of two sprays of fungicide were sufficient to provide preventive control (>90%). The susceptibility of inflorescence varied with its developmental stage. Proper forecasting reduced the number of sprays from 7 to 2 or 3. There was no varietal difference in incidence of the disease or response to fungicide applications. During the course of this study, we identified seedling plants which consistently showed resistance to powdery mildew.

Seedlings recovered from underdeveloped seeds of different commercial cultivars of Citrus were studied for their ploidy level. Cytological examination revealed that maximum triploid plants were found in lime Kaghzi (15.5%) followed by grapefruit Foster, mandarin Kinnow, sweet orange Musambi and mandarin Feutrell's Early (7.3%). Lime also produced the highest percentage of tetraploids (9.1%) followed by mandarin Kinnow and grapefruit Foster, while the minimum was found in mandarin Feutrell's Early. The polyploids were transplanted in pots and after hardening they were grown in the greenhouse for further morphological and genetic assays. 125chlorobenzene for 2-3 h at 20-26°C. Then they were dipped in fixative (100% ethyl alcohol, glacial acetic acid and chloroform in 6:1:3) for 10-12 h at 4°C. After fixation samples were washed with sterilized water. For microscopic observation the material was hydrolyzed with 5M HCl at 25°C for 20 min. Samples were dipped in Mordant solution containing 4% FeNH 4 (SO 4 ) 2 12 H 2 O for 1 h and washed 4-5 times with sterilized water. Samples were stained with 0.5% hematoxylin dye for 2-4 h (Gmitter et al. 1990). Prepared squashes were observed under Nikon inverted microscope at 10× × 100× magnification. After cytological confirmation diploids were discarded. The polyploids were transplanted in pots filled with sterilized substrate containing sand, silt and farmyard manure (2:1:1). When seedlings obtained 10-15 cm height, they were planted in the greenhouse. The experiment was laid out in Completely Randomized Design (CRD). Every cultivar included 3 randomized plots. Data were analyzed statistically with Duncan's Multiple Range Test (Steel, Torrie 1980). RESULTS AND DISCUSSION Seed size and germination percentageCitrus cultivars were examined for seed size viz. developed and underdeveloped. Significantly higher numbers were found in grapefruit cv. Foster (10 seeds) for developed seeds and in mandarin cv. Kinnow (17 seeds) for underdeveloped seeds (Table 1). The results are strengthened because triploids were obtained from underdeveloped seeds ranging 1/3 to 1/6 of size of developed seeds yielding mostly diploids (Esen, Soost 1973a,b). 1 haploid, 18 diploids and 51 triploids were found in plants originating from 82 underdeveloped seeds out of 2,049 seeds from pummelo cultivar Banpeiyu crossed with grapefruit (Toolapong et al. 1996). Maximum germination percentage was found in Musambi (42.5%) followed by Kaghzi (35.5%), while minimum germination was observed in Feutrell's Early (25.0%), Foster (29.5%) and Kinnow (35.3%). Plant growth in Citrus cultivars Diploid seedlingsRegarding total plant growth, results were found highly significant for diploid seedlings. Maximum plant growth was observed in Foster grapefruit plants (12.38 cm), followed by Musambi sweet orange, Feutrell's Early mandarin and Kaghzi lime (10.02 cm). Seedlings of mandarin cv. Kinnow depicted the least growth (9.44 cm) of all investigated cultivars (Table 2). Diploids are reported to grow more rapidly (Khan...

ABSTRACT. Due to increased global concern over the deleterious effects of toxic heavy metals in the environment, it has become necessary to develop plant genotypes that limit the uptake of heavy metals to aerial edible parts. To address this concern, we performed a glasshouse experiment to assess variations within tomato germplasm for cadmium (Cd) tolerance under control conditions and under simulated stress conditions. Significant differences (P < 0.01) were observed among all genotypes at both Cd levels (3 ppm and 6 ppm). Our analyses showed that the genotypes 9086, Roma, Sitara TS-01, pak0010990, CLN-2123A, Picdeneato, 0.006231, and 7035 gave the best yields with minimum Cd content in their fruit, whereas the genotypes 42-07, 17883, BL-1176-Riostone-1-1, Marmande, and 17882 had relatively low yields with higher metal contents. The heavy metal was found to accumulate first in the shoot, then fruit, leaf, and finally root in tolerant genotypes; in susceptible genotypes, the order was fruit, shoot, leaf, and root. The inter-genotype differences in Cd uptake indicated the possibility of manipulating tomato genotypes to develop Cd tolerant tomato varieties or hybrids that allow safe use of a tomato crop grown on Cd contaminated soils.

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