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The objective in this study was to verify the efficiency of different procedures for evaluating the physiological potential of bell pepper seed and identify its relationship with germination at different temperatures and with seedling emergence. Five seed lots each of the Reinger and Sentinel hybrids were used. Seed physiological potential was evaluated by germination, saturated salt accelerated aging (48 h/41 °C), seedling emergence (percentage and speed), and tetrazolium tests (preconditioning at 45 °C/3 h and seed staining at 45 °C/2 h). Germination (percentage and speed) on a thermogradient table at 15 °C, 18 °C, 21 °C, 25 °C and 30 °C was also evaluated the saturated salt accelerated aging and tetrazolium tests are suitable for access the physiological potential of bell pepper seeds. It was also confirmed that vigorous seed lots perform better when exposed to different temperatures during germination.

Acceleration of the growth rhythm of plants using nitrogen fertiliser alters the rates of physiological processes like growth and senescence and may cause significant changes in sward structure, interfering with plant and animal responses. The objective of this experiment was to evaluate sward structure of marandu palisadegrass (Brachiaria brizantha) maintained at 30 cm under continuous stocking and subjected to contrasting rhythms of growth from January 2007 to April 2008. These were generated using or not nitrogen fertiliser, and comprised four experimental treatments as follows: control (non-fertilised), 150, 300 and 450 kg ha-1 of N. Acceleration of the growth rhythm of plants was associated with increases in leaf and stem bulk density, and resulted in larger LAI and total bulk density on swards subjected to faster (fertilised with 300 and 450 kg ha-1 of N) than those subjected to slower rhythms of growth (non-fertilised or fertilised with 150 kg ha-1 of N). Variations in dead material bulk density were associated with seasonal variations in climatic conditions, and were not influenced by growth rhythms. During autumn/winter and early spring (dry period of the year) swards subjected to faster, relative to those subjected to slower rhythms of growth, had larger proportion of leaves on the top horizons. On the other hand, sward structure did not vary among rhythms of growth at times of the year when there was no limitation in the availability of climatic growth factors (late spring and summer), indicating that when control of the grazing process is efficient, changes in sward structure are basically a function of seasonal variations in climatic growth conditions and phenological state of plants.

The degradation of Brachiaria decumbens Stapf. (Signal grass) pastures has resulted in a big problem for the Brazilian cattlemen. The objective of this study was to assess fertilization with nitrogen (N) and sulphur (S) rates on yield of Brachiaria brizantha (Hochst. ex A. Rich.) Stapf. cv. Marandu (Marandu palisadegrass) under establishment in a soil supporting degrading pasture of Brachiaria decumbens Stapf. Additionally, the N and S concentrations in plant tissue and soil according to the rates of these nutrients were evaluated. The study was carried out in a greenhouse in pots filled with an Entisol with high organic matter content. Five rates of N (0; 100; 200; 300 and 400 mg dm-3) and five rates of S (0; 10; 20; 30 and 40 mg dm-3) were tested in a 52 fractionated factorial. Plants were harvest three times. The interaction N rates × S rates was significant for the variables leaf area, tiller number, shoot dry matter, N concentration and N:S ratio in plants, and total N and sulphur-sulphate in the soil in at least one of the three growth periods of Marandu palisadegrass in establishment. The supply of both S and N to reach the N:S ratio about 10:1 in the fertilization promoted high yield, adequate N and S concentrations for plant metabolism and forage production, as well as kept and/ or raised the soil fertility in relation to these nutrients.

Mondo V.H.V.,University of Sao Paulo | de Carvalho S.J.P.,University of Sao Paulo | Dias A.C.R.,University of Sao Paulo | Filho J.M.,USP ESALQ
Revista Brasileira de Sementes | Year: 2010

Brazil has the largest number of native species of Digitaria in the Americas. This genus is considered as a weed causing problems in various economic crops and can be found throughout Brazil in many different ecological situations. The object of this research was to evaluate the effects of light and temperature on the seed germination of four Digitaria weed species. The experiment was conducted in germination chambers using a factorial 4 x 2 scheme of treatments under four temperatures (25 °C constant, alternating 20-30 °C, 20-35 °C and 15-35 °C) with alternate light cycles (8h light/16h darkness) or absolute darkness. The weed species studied were Digitaria horizontalis Willd., D. bicornis (Lam.) Roem. & Schult., D.ciliaris (Retz.) Koel. and D. insularis (L.) Fedde. The percentage and speed of germination were evaluated up to 21 days after the start of the germination test. The four species showed differing seed physiological responses. D. bicornis and D. horizontalis required light for germination while D. ciliaris and D. insularis did not. The best temperatures for germination are 20-35 °C for D. bicornis and D. ciliaris, and 20-35 °C or 15-35 °C for D. horizontalis and D. insularis.

Maize (Zea mays L.) elite inbred lines developed from pedigree programs tend to be genetically related. Therefore, it is necessary to incorporate unrelated inbreds to those programs to allow the continued release of outstanding single-crosses. The objectives of this research were to compare the usefulness of a modified reciprocal recurrent selection procedure (MRRS) to improve populations to be used as sources of elite inbreds and outstanding single-crosses to integrate pedigree programs, and to investigate the effects of selection on the relative contribution of general (GCA) and specific combining (SCA) abilities to the single-crosses variation. Eight and six S3 lines from populations IG-3-C1 and IG-4-C1, respectively, selected from the first cycle of the MRRS program were crossed in a partial-diallel mating design, and the 48 experimental and five commercial single-crosses were evaluated in six environments. Grain yield mean of the experimental single- crosses (9.57 t ha-1) did not differ from the commercial single-crosses (9.86 t ha-1), and ten of the 48 experimental single-crosses could be released as cultivars because they compared favorably to the currently used single- crosses. Thus, one cycle of the MRRS procedure improved efficiently the populations allowing the development of outstanding single-cross, but additional cycles of selection should be carried out since none of the experimental single-crosses outperformed the highest yielding commercial single-cross. The relative contribution of the GCA over SCA may have been affected by the MRRS, since the SCA was more important than GCA for some of the traits assessed.

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