S U M M A R YInvestigations are reported of root and shoot growth in semi-dwarf and taller winter wheat varieties grown in contrasting soils over three years. Comparisons were made of the distribution with depth of roots, estimated by injecting rubidium-86 into stem bases and counting the content in soil cores. The relative ability to absorb phosphate from different zones was

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The growth and development of two semi-dwarf winter wheat varieties, of two taller varieties, and of random selections from two crosses between semi-dwarf and taller varieties were compared over 2 years. Changes with time of crop dry weight/m 2 , leaf area index and ear size were expressed as orthogonal polynomial regression coefficients. Significant correlations were obtained between yield, the polynomial coefficients and growth measurements relating to number of tillers and flag leaf area duration, but many of these variables were significantly correlated with each other. Multiple regression equations were therefore calculated expressing yield in terms of the variables. These showed flag leaf area duration and rate of ear growth to be the most important characters determining crop yield. The greatest reduction in total yield variance was obtained by the simultaneous consideration of characters relating to photosynthetic capacity and ear development. The significance of this finding in relation to the relative importance of 'source' and 'sink' in determining grain yield are discussed. TM __ r . TYTTr , rrT _-T port that the high yields obtained from the semidwarf varieties Games and Nugaines in Washington Outstanding successes have been achieved in State, U.S.A., were not obtained when these many countries in breeding high-yielding spring and varieties were grown in areas of lower rainfall, but winter varieties of semi-dwarf wheats (Borojevic, Subbiah et al. (1968) and Lupton et al. (1974Lupton et al. ( ) report 1908Briggle & Vogel, 1968;Swaminatham, 1968; that there is little difference in their patterns of Borlaug, 1969). Numerous experiments have also root development. been made to determine the physiological factorsThe high yields of the semi-dwarf wheats cannot upon which the performance of these varieties arise directly as a result of their higher harvest depends. These have shown the importance of high index, because it has been shown by Thorne (1965) tillering capacity (Paquet, 1968) and of differences that the greater part of the carbohydrate utilized in photosynthetic rate and leaf angle (Lupton, in filling the grain in wheat is synthesized during 1972). Experiments have also shown that the gib-the period after ear emergence, that is, after the berellic acid content of dwarf and semi-dwarf stems have achieved their final length. The possivarieties is greater than that of taller varieties (Gale bility remains, however, that yielding capacity may & Marshall, 1973;Radley, 1970) though its normal be partly determined by the capacity of the ear to effect in causing stem elongation is limited by an store carbohydrate, and that this may be deterinhibitor. Fisher (1973) andHolmes (1973) suggest mined by the carbohydrates available at the time the that the high yield of the semi-dwarf wheats is ear itself is growing most rapidly, shortly before associated with delayed development of double ear emergence (Bingham, 1972). ridges during the ontogeny of the ear, but these The purpose of the experiments described ...

S U M M A R Y Screening tests exposed varietal differences in the tolerance of winter wheat to high doses of the wild oat herbicides difenzoquat and diclofop-methyl. Subsequent yield trials at recommended and higher doses confirmed the sensitivity of Score and Sportsman to difenzoquat and showed Atou, Bouquet and Hobbit to be less tolerant than some other varieties. In most varieties, earlier spraying proved safer than treatment at or beyond the beginning of jointing. Varietal differences with diclofop-methyl were smaller and inconsistent.Crops damage from these two herbicides was more severe in another experiment the following season, in which isoproturon at double the recommended dose also caused severe damage but flamprop-methyl was fairly well tolerated by all varieties.

The current study aimed to verify the effect of the inoculant constituted by diazotrophic bacteria applied in different ways, associated to different nitrogen (N)-fertilizer doses, on the yield and N utilization efficiency of sugarcane ratoon. The use of inoculant did not affect the N content in leaves, the chlorophyll content, tiller number, stalk diameter, or any of the other assessed technological attributes. However, the use of inoculant associated to doses of 60 and 90 kg N ha ¡1 promoted increase in stalk yield, dry matter, and N accumulation and efficiency of N fertilizer, and, on the other hand, the association of inoculant with 120 kg N ha ¡1 caused reduction of these parameters.

SUMMARYWinter wheat varieties were treated with the wild‐oat herbicides difenzoquat and diclofop‐methyl at several growth stages in a series of four field experiments.High rates of difenzoquat damaged the winter wheat varieties Bouquet, Sportsman, Hobbit and Maris Huntsman but not Hustler. Treatment of the sensitive varieties during tillering stimulated excessive tiller production, resulting in more ears with fewer and smaller grains than on the unsprayed controls; later applications reduced the number of grains and severely depressed yield.In contrast, the early applications of diclofop‐methyl, during tillering, were more damaging than the later ones. Bouquet was more tolerant of diclofop‐methyl than were the other varieties tested.

-This study aimed to evaluate the tolerance of sugarcane cultivars to ratoon eradication under different glyphosate rates by means of physiological responses. Therefore, a trial was carried out in randomized complete blocks with 4 x 4 factorial design (cultivars x rates) totaling 16 treatments with four replicates. The cultivars IAC91-5155, IACSP93-3046, and IAC86-2480 and IAC87-3396 and the glyphosate rates 0 g ha were tested. The variables analyzed were percentage of tiller mortality, quantum efficiency of PSII (Fv/Fm) and SPAD index. The results showed that there are differences among sugarcane cultivars for tiller eradication and for physiological responses with glyphosate different rates. The rate of 2,880 g hawas the most efficient in eliminating sugarcane tillers. The cultivars IAC86-2480, IAC87-3396 and IACSP93-3046 were the most sensitive and the IAC91-5155 tolerated, for a longer period of time, the damage to the photosynthetic apparatus of the ratoons caused by glyphosate desiccation. Due to different responses, different managements should be considered for eliminating ratoons of different cultivars.Keywords: Saccharum spp., varieties, tillers, chlorophyll fluorescence, SPAD, herbicide. IAC91-5155, IACSP93-3046, IAC86-2480 RESUMO -O presente trabalho teve como objetivo avaliar a tolerância de cultivares de cana-deaçúcar à erradicação de soqueiras com diferentes doses de glyphosate por meio de respostas fisiológicas. Para isso, um ensaio foi desenvolvido no delineamento experimental de blocos ao acaso em esquema fatorial 4 x 4 (cultivares x doses), totalizando 16 tratamentos com quatro repetições. Foram utilizados os cultivares