Specificity of potential contamination of rice checks with weed seeds

Goal. To analyze the potential level of contamination of arable soil layer weed seeds and to establish the specificity of the changes in such reserves during the vegetation period of crops. The study was performed on rice checks of the Institute of rice of NAAS in the Kherson region in the 2017—2019 biennium. Methods. Research field, small and laboratory. To determine the factor of seeds and vegetative reproductive organs of weeds in certain soil horizons of rice fields per unit area (pieces/m2) was selected soil samples by the method of A. N. Kiseleva — twice per season, in spring and after harvest of rice. The arable soil was divided into three layers (10 cm each). To determine the viability of seeds used method of staining their tetrazoles. The results were compiled and analyzed. Results. A comparison of the level of potential contamination between horizons showed the highest number of weed seeds in the horizon of 0—10 cm on average, 16041 pieces/ m2, which is 47.6% of the overall presence of weeds in the soil (33650,2 pieces/ m2). In the soil horizon 10—20 cm the number of weed seeds reached 10489.2 pieces/m2, or 31.2% of the debris of the upper horizon. In the lower horizon of 20—30 cm level of the presence of weed seeds was low — 7119.8 pieces/ m2, which amounts to 21.2% from that of the top horizon of the soil. Among the weed species whose seeds were present in soil samples of the top horizon of 0—10 cm, the largest part was Kuga Astrakhantseva Scirpus mucronatus L. — 59.8%, in another place Boule seeds Kuga razveseloj Scirpus supinus L. — 31.8%, Polygonum Persicaria hydropiper L. percetage — 1004.7 pieces/ m2 (6,3%), chicken millet Echinochloa crus galli L. — 329.1 pieces/m2 (2.1%). Other types were less in the stocks of weed seeds. Conclusions. During the vegetation period inventory quantities of seeds of change and by autumn are increasing. The largest amplitude value of the stock of weed seeds is manifested in the upper 0—10 cm horizon of the arable layer and reaches to 12.3%. Qualitative and timely implementation of measures to protect rice crops from sowing to the presence of weeds provides a gradual reduction in the volumes of their Bank of seeds in the soil.

FITOSSOCIOLOGIA E SUPRESSÃO DE PLANTAS DANINHAS SOB EFEITO DA SOLARIZAÇÃO E COBERTURA COM CAPIM-ELEFANTE

A técnica de solarização e da cobertura vegetal são estratégias de manejo de plantas daninhas importantes para reduzir a mão-de-obra e outras limitações impostas pelo controle mecânico, porém a eficiência e resposta na composição florística desses métodos varia conforme manejo realizado na agricultura familiar. Dessa forma, o objetivo desse trabalho é avaliar o efeito supressivo da solarização e cobertura com capim-elefante (Pennisetum purpureum Schum.) sobre a emergência de plantas daninhas, bem como identificar e quantificar as espécies daninhas presentes através do levantamento fitossociológico. O experimento foi conduzido a campo no ano agrícola 2017/2018, utilizando delineamento experimental em blocos casualizados e quatro repetições. Os tratamentos foram dispostos em esquema fatorial, onde o fator A compara a solarização (presença e ausência); e o fator B a cobertura com capim-elefante (sem e com). Realizou-se o levantamento fitossociológico e avaliação da massa seca da parte aérea das plantas daninhas em resposta aos tratamentos. A adição do capim-elefante na superfície do solo atua como supressor da diversidade de plantas daninhas, como Ageratum conyzoides, Urochloa plantaginea, Galinsoga parviflora, Polygonum persicaria, Spermacoce latifolia, Sida sp. e Stachys arvensis. Enquanto que a solarização, aumenta o valor de importância do Cyperus sp. nas parcelas sem a utilização da cobertura vegetal. Ainda, a solarização realizada por 20 dias não foi eficiente para o controle das plantas daninhas.

Eficiência e deposição de herbicidas na cebola em função do adjuvante e da taxa de aplicação

Objetivou-se, com este trabalho, avaliar o efeito da taxa de aplicação e do uso de adjuvante sobre o controle de plantas daninhas e deposição dos herbicidas ioxynil + clethodim em plantas de cebola. O experimento consistiu em seis tratamentos com cinco repetições, arranjados em esquema fatorial 2 x 3, ou seja, a combinação de dois níveis de adjuvante (com e sem) com três taxas de aplicação (100, 150 e 200 L ha-1). Os tratamentos foram aplicados em pós-emergência, após o enraizamento da cebola e quando as plantas daninhas se apresentavam no estádio de quatro a seis folhas. Os tratamentos não promoveram fitotoxicidade na cultura da cebola. Houve tendência de melhoria no controle de Cyclospermum leptophyllum e Polygonum persicaria com o uso do adjuvante, contudo não houve significância. A deposição de calda não foi afetada pela taxa de aplicação e pelo uso de adjuvante. Conclui-se que o uso de adjuvante e a redução da taxa de aplicação não comprometeram a eficiência e a deposição dos herbicidas ioxynil + clethodim.

DNA methylation mediates genetic variation for adaptive transgenerational plasticity

Environmental stresses experienced by individual parents can influence offspring phenotypes in ways that enhance survival under similar conditions. Although such adaptive transgenerational plasticity is well documented, its transmission mechanisms are generally unknown. One possible mechanism is environmentally induced DNA methylation changes. We tested this hypothesis in the annual plant Polygonum persicaria , a species known to express adaptive transgenerational plasticity in response to parental drought stress. Replicate plants of 12 genetic lines (sampled from natural populations) were grown in dry versus moist soil. Their offspring were exposed to the demethylating agent zebularine or to control conditions during germination and then grown in dry soil. Under control germination conditions, the offspring of drought-stressed parents grew longer root systems and attained greater biomass compared with offspring of well-watered parents of the same genetic lines. Demethylation removed these adaptive developmental effects of parental drought, but did not significantly alter phenotypic expression in offspring of well-watered parents. The effect of demethylation on the expression of the parental drought effect varied among genetic lines. Differential seed provisioning did not contribute to the effect of parental drought on offspring phenotypes. These results demonstrate that DNA methylation can mediate adaptive, genotype-specific effects of parental stress on offspring phenotypes.