Relationships of Photosynthetic Photon Flux Density, air Temperature and Humidity with Tomato Leaf Diffusive Conductance and Temperature

The objective was to study the leaf temperature (LT) and leaf diffusive vapor conductance (gs) responses to temperature, humidity and incident flux density of photosynthetically active photons (PPFD) of tomato plants grown without water restriction in a plastic greenhouse in Santa Maria, RS, Brazil. The plants were grown in substrate and irrigated daily. The gs was measured using a steady-state null-balance porometer on the abaxial face of the leaves during the daytime. Both leaf surfaces were measured in one day. The PPFD and LT were measured using the porometer. Leaf temperature was determined using an infrared thermometer, and air temperature and humidity were measured using a thermohygrograph. The leaves on the upper layer of the plants had higher gs than the lower layer. The relationship between the gs and PPFD was different for the two layers in the plants. A consistent relationship between the gs and atmospheric water demand was observed only in the lower layer. The LT tended to be lower than the air temperature. The mean value for the gs was 2.88 times higher on the abaxial than adaxial leaf surface.

Efeito de restritores hídricos sobre a germinação, comprimento da radícula e níveis de detecção de Colletotrichum gossypii var. cephalosporioides em sementes de algodão

O fungo Colletotrichum gossypii var. cephalosporioides, agente causal da ramulose do algodoeiro, é transmitido pela semente que se constitui em uma das mais importantes fontes de inóculo inicial e de introdução da doença em áreas indenes. Para que se possa identificar sua presença em lotes de sementes, é importante que se empreguem métodos de detecção rápidos e seguros. O mais empregado é o do papel de filtro, que se baseia na avaliação de sinais do patógeno desenvolvidos sobre as sementes, seguida da sua identificação morfológica. O método apresenta a desvantagem do crescimento das plântulas no período de incubação das sementes que pode favorecer o desenvolvimento de outros fungos e prejudicar a caracterização do patógeno. Para minimizar este problema vem sendo empregada a técnica da restrição hídrica. O presente trabalho teve como objetivo avaliar o efeito de três solutos em dois potenciais osmóticos, comparados ao tratamento padrão de água destilada, ao congelamento e ao 2,4 D, sobre a germinação, comprimento da radícula e detecção do agente causal da ramulose, durante o teste de sanidade. Os solutos Manitol e NaCl foram mais eficientes em inibir a germinação e favorecer a incidência do patógeno no potencial osmótico de -0,8 MPa. O KCl mostrou-se eficiente em inibir a germinação nos dois potenciais osmóticos testados, -0,6 e -0,8 MPa, porém reduziu a incidência do patógeno no potencial de -0,8 MPa. Os solutos Manitol, nos potenciais osmóticos de -0,8 e -0,6 MPa e o NaCl no potencial osmótico de -0,8 foram eficientes em reduzir o comprimento da radícula, sem interferir negativamente nos níveis de detecção de C. gossypii var. cephalosporioides, podendo ser recomendados para uso em análises sanitárias de rotina.

Relationships of photosynthetic photon flux density, air temperature and humidity with tomato leaf diffusive conductance and temperature

The objective was to study the leaf temperature (LT) and leaf diffusive vapor conductance (gs) responses to temperature, humidity and incident flux density of photosynthetically active photons (PPFD) of tomato plants grown without water restriction in a plastic greenhouse in Santa Maria, RS, Brazil. The plants were grown in substrate and irrigated daily. The gs was measured using a steady-state null-balance porometer on the abaxial face of the leaves during the daytime. Both leaf surfaces were measured in one day. The PPFD and LT were measured using the porometer. Leaf temperature was determined using an infrared thermometer, and air temperature and humidity were measured using a thermohygrograph. The leaves on the upper layer of the plants had higher gs than the lower layer. The relationship between the gs and PPFD was different for the two layers in the plants. A consistent relationship between the gs and atmospheric water demand was observed only in the lower layer. The LT tended to be lower than the air temperature. The mean value for the gs was 2.88 times higher on the abaxial than adaxial leaf surface.

Hydric restriction as vigor assessment method of soybean seeds

The objective of this study was to investigate the possibility of using hydric restriction as a method for evaluating vigor of soybean seeds. The soybean seeds, cultivar BRS 245RR, represented by four different seed lots, were characterized by germination and vigor. For the treatment of hydric restriction and temperature, the combination of substrate water potential and temperature were the following: deionized water (0.0 MPa); polyethylene glycol (PEG 6000) aqueous solution (-0.1, -0.3 and -0.5 MPa); and four temperatures (20 ºC, 25 ºC, 30 ºC, and 35 ºC), respectively. A completely randomized experimental design was used, with four replications per treatment, and the ANOVA was performed individually for each combination of temperature and water potential of substrate. According to results obtained, the test of hydric restriction has the same efficiency of the accelerated aging test in estimating vigor of soybean seeds, cv. BRS 245RR, when water potentials of -0.1 MPa or -0.3 MPa at a temperature of 25 ºC, or -0.3 MPa at a temperature of 30 ºC are used.