Tillering dynamics in spring and summer of marandu palisade grass pastures previously used under deferred grazing

ABSTRACT This work was conducted to evaluate the effect of deferred pasture condition of Brachiaria brizantha cv. Marandu in the late winter on tillering during the growing season. The treatments were three pasture conditions at late winter: short pasture, tall pasture and tall/mown pasture. In September and October, tiller appearance rate (TApR) and tiller mortality rate (TMoR) were greater in the tall/mown pasture. In November and December, tall pasture presented greater TApR. From November to January the TMoR was greater in the tall pasture. The tiller stability index of short and tall/mown pastures were greater in October. The short pasture presented a greater tiller number than the tall and tall/mown pastures during the entire experimental period. Deferred and short pasture of marandu palisade grass at late winter presents in general lower tiller mortality and higher population density of tillers from the early spring onwards, in comparison to tall pasture. The mowing of marandu palisade grass with high forage mass at the late winter, although it only temporarily compromises the population stability of tillers, also stimulates its fast tillering from spring on.

Source–sink relationships during early crop development influence earliness of sugar accumulation in sugarcane

The dynamics of tiller production and senescence modify early source–sink relationships in sugarcane and the thermal time from crop emergence to the end of the tiller mortality phase appears to be a key trait in identifying earliness of sucrose accumulation.

Marandu palisade grass management strategies at the beginning of the deferment period and effects on tillering

Pasture mowing at the beginning of deferment stimulates tillering and can be used in different ways. The aim of this study was to understand how the mowing of Urochloa brizantha cv. Marandu Syn. Brachiaria brizantha cv. Marandu (marandu palisade grass) prior to the deferment period modifies tillering activity and the characteristics of young, mature, and old tillers. Three mowing strategies were evaluated: canopies kept at a height of 15 cm for five months before deferment (15/15 cm); canopies kept at 30 cm (30/15 cm) or 45 cm (45/15 cm) for five months before deferment and posteriorly cut to 15 cm at the start of the deferment period. The structural characteristics of young, mature, and old tillers of marandu palisade grass were compared only at the end of the deferment period. The tiller appearance rate was greater before (16.0%) than during (6.4%) the deferment period, but a contrasting response pattern was observed for the tiller mortality rate. The defoliation strategies that resulted in greater numbers of tillers in the canopies were 30/15 cm (2,098 tillers m-²) and 45/15 cm (2,160 tillers m-2). The defoliation strategy that generated the greatest percentage of young tillers in the canopy was 45/15 cm (26.1%), while the percentage of old tillers was greater in the canopies submitted to the 15/15 cm (64.1%) and 30/15 cm (61.5%) strategies. Weight and percentage of live stems of mature and old tillers were greater in relation to young tillers. The percentage of live leaves was grater in young tillers (52.6%), intermediate in mature tillers (41.4%), and lower in old tillers (21.3%). Regarding the percentage of dead leaves, the opposite trend was observed, where the percentage was greater in the old than in young tillers. Leaf area was greater in mature tillers (55.3 cm²) than in old tillers (29.2 cm²). Mowing of the marandu palisade grass to 15 cm at the beginning of the deferment period increases the number of young tillers, which have a more favorable morphological composition than mature and old tillers.

Sugarcane tolerance to ratoon eradication with glyphosate determined by physiological responses

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-1; 1,920 g ha-1; 2,400 g ha-1; 2,880 g ha-1 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 ha-1 was 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.

Effects of fire, post-fire defoliation, drought and season on regrowth and carbohydrate reserves of alpine snowgrass Poa fawcettiae (Poaceae)

Following defoliation, grasses regenerate foliage from basal buds. We used a combination of field, glasshouse and growth-room experiments to investigate the role of carbohydrate reserves in regrowth of Poa fawcettiae Vickery following fire or mock grazing, and the effect on reserve dynamics of post-fire defoliation, drought and seasonal factors. Fructan reserves of burnt plants were depleted during foliage regeneration, and remained below those of unburnt plants for up to 10 months in the field, and for up to 3 months in the glasshouse. Plants were resilient to occasional mechanical clipping of foliage, but experienced significant depletion in fructan reserves and high tiller mortality when clipped at frequent intervals. Cold treatment led to fructan concentrations almost double those in plants growing at a warm temperature, explaining peak autumn levels in field plants, whereas a short drought treatment doubled the concentration of ethanol-soluble carbohydrates. Taken together, these data show how the dynamics of carbohydrate reserves, and specifically tiller-base fructan reserves, explain the vegetative regeneration capacity of P. fawcettiae.

Evaluation of Resistance to Chinch Bug in Pearl Millet in Temperate and Subtropical Environments

Pearl millet inbreds and hybrids were evaluated for resistance to chinch bug at Lincoln, NE, and Tifton, GA, in 2003 and 2004. Insect feeding damage expressed as plant mortality, stunting, leaf sheath necrosis, and tiller mortality was observed over time. Resistance was expressed by a slower rate of plant damage to resistant genotypes compared to susceptible ones. Across experiments, inbreds 59464B and 59668M-1 were most frequently identified as resistant. Inbred Tift 99B was susceptible in every experiment and by every assessment criterion. The experiments revealed information on the genetic expression of resistance. When insect damage among hybrids made with Tift 454 was compared, resistance tended to be dominant or overdominant in expression. Evidence for location-specific resistance caused by environmental conditions or genetic differences in the insect populations between the two locations was observed. Inbreds 03GH707 and Tift 454, developed at Tifton, were resistant only in some assessments at Tifton, but not at Lincoln. 16RmR1, developed at Lincoln, was susceptible in both Lincoln experiments, but not at Tifton. 03GH706 was susceptible in some Tifton assessments, but was not among the most susceptible inbreds in the Lincoln experiments. Evaluations are needed at multiple locations to effectively identify resistance to damage caused by chinch bug feeding in pearl millet. Accepted for publication 14 October 2008. Published 12 January 2009.

Wheat development as affected by nitrogen and sulfur nutrition

Sulfur (S) is one of the essential nutrients for crop growth, which is linked to nitrogen (N) in many physiological functions. The rate of leaf emergence (RLE) and final leaf number (FLN) determine the duration of the emergence (Em)–anthesis (Ant) period in wheat. Although some studies showed effects of N and phosphorus on RLE and the length of the Em–Ant period, no reports studied the effect of N and S interaction on the phasic development and the coordination of RLE with tillering appearance. A bread-wheat genotype was grown with 4 N and 2 S fertiliser rates during 2000 and 2001 in field plots. In addition, an experiment with 4 combinations of N and S rates (N0S0, N0S1, N1S0, and N1S1) was arranged in containers using nutrient solutions in 2001. Under field conditions, additional N and S did not modify the duration of the different phenological stages or the Phy value and FLN. However, the stronger N and S deficiency in the experiments conducted in containers affected RLE. A higher S rate delayed the period Em–Ant by 65° degree-days under no N restrictions, mainly by a delay in the duration of terminal spikelet (TS)–Ant period. Phyllochron (Phy) changed with crop ontogeny (inflection point occurred on 7th leaf) and N and S did not affect the timing when Phy changed; however, a lower N supply increased Phy in earlier leaves without effect of S on this trait. Treatments without S or N deficiency achieved the highest maximum tiller number (MTN) and the greatest tiller mortality rate (TMR); however, tiller number at maturity was 76% higher in this treatment with respect to the rest of the treatments because of the MTN attained. The number of tillers per emerged leaf was significantly increased when plants were grown under high N supply. Under no N restrictions, additional S increased the number of tillers per emerged leaf by 24%.