Germinação de sementes e crescimento de plântulas de algodoeiro (Gossypium hirsutum L.) sob diferentes concetrações de cobre

Abstract

Cotton cultivation is a highly technical agricultural activity, which requires massive use of sources containing micronutrients. The excessive use of fertilizers, as well as swine manure, can contribute high concentrations of copper to the soil, causing toxicity to cultivated plants. The objective of the present work was to analyze the effect of different concentrations of copper on the germination and growth of shoots and roots of cotton seedlings. The test was carried out in a split-plot scheme in randomized blocks, with cross classification and 4 replications. The seeds were divided into 4 lots of 16 repetitions of 50 seeds and each repetition was sown on paper substrate for germination, previously moistened with a volume of water corresponding to 2.5 times the weight of the paper. The water used for soaking the 4 lots was added with different concentrations of CuSO4, so that the final copper concentrations were 0.0, 100, 200 and 300.0 mg/L, generating four different treatments. The paper rolls were kept in germinators at a constant temperature of 25ºC and a constant photoperiod of 24 hours, and the evaluations were carried out in 4 repetitions of each treatment, randomly removed from the germinator on the fifth, sixth, seventh and eighth days after sowing. Germination, growth and dry mass evaluations were carried out on the fifth, sixth, seventh and eighth day after sowing. In the evaluation of germination, seeds that showed radicle growth of 1 mm were considered germinated, eliminating abnormal seedlings and hard and dead seeds, and the data were converted to the percentage of normal seedlings. The growth evaluations were carried out with the aid of a millimeter ruler, measuring the length of the primary root and shoot, with the results expressed in cm seedling-1. To evaluate the dry mass, the wet material was dried in an oven with forced air circulation, at 80°C for 24 hours, after which the dry material was weighed. Analysis of variance (99% F test) was used to analyze the variables. Comparisons of the mean of each repetition were performed using Tukey's multiple comparison test or regression, both at 99% confidence. Copper affected the germination rate at the highest concentration tested (300mg/L), from the second evaluation, the concentrations of 100 and 200mg/L, affected the fourth day of evaluation. The different concentrations did not affect the germination speed index. For the abnormal seedling variable, there was no significant interaction between the factors days and concentrations of copper, showing that the factors occur independently. Root length was the variable most affected by copper treatment. As for the length of the aerial part, the metal had no influence on its size. Copper affected the dry mass weight of cotton seedlings.