Physiological factors that control the growth of wheat grains are not well known. To evaluate the grain weight potentials and post-flowering source limitation, this study was carried out in climatically conditions of Neyriz in 1995 growing season. The design of the experiment was split plot with four replications. The main plots included four planting dates (6th Nov., 22nd Nov., 7th Dec. and 22nd Dec.), and the sub plots included three wheat cultivars (Roshan, Falat and Ghods). Assimilate increase for grain growth was done through decreasing the number of spiklets. In each spike, four spike lets with numbers 3, 6, 9 and 12 were kept and others were left out. The results indicated that source limitation increased with delaying the planting practice, in such a manner that the grains produced in the delayed planting date faced with a limitation of about 44.2%; whereas the limitation for the first planting date was 4.8%. On the other hand, comparison among cultivars showed that source limitation average for Roshan cultivar was less than Falat and Ghods. The source limitations for above-mentioned cultivars were 13.6%,20.6% and 22.9%, respectively.

In order to study the effects of heat stress after anthesis on source limitation of six wheat (Stork, Showa, Green, Star, Chamran and Fong) and two barley (Jonob and Sarasary 6) cultivars, two field experiments were conducted in delayed and optimum sowing dates. Plants in delayed sowing date experienced heat stress in after anthesis growth stage. Study of grain yield indicated that the highest grain yield was in Jonob in both conditions. Source limitation difference in experiments, cultivars in experiments and interaction between cultivars and experiments was significant in 1% probability level. Mean of source limitation in optimum and heat stress conditions was 12.5% and 25.5% respectively. Higher source limitation in late maturity cultivars such as Green and Star was related to delay in anthesis and contact of grain growth period with heat stress. In early mature cultivars such as Fong with early anthesis, grain growth period was before heat conditions, while source limitation and also grain yield and grain weight reduction was the lowest in Fong cultivar.

In order to determine the effect of source-sink limitation on yield and yield components of four rice cultivars, an experiment was conducted at Rice Research Institute of Iran, Deputy of Mazandaran (Amol) in 2003. The experiment was in factorial based on randomized completely block design with four replications. The studied factors were source-sink limitation in four levels (cutting of all leaves except flag leaf; cutting of flag leaf; cutting of 1/3 end of panicle; control) and cultivars in four levels (Tarom; Neda; Shafagh; Fajr). Some traits such as grain yield, harvest index, grain number per panicle, unfilled grain number per panicle, panicle length, panicle fertility and 1000 grain weight in different source-sink limitation treatments were investigated. Results showed that imposing of different source-sink limitation treatments had a positive effect on all mentioned traits. Interaction effect between cultivar and source-sink limitation was also significant. The control and cutting of 1/3 end of panicle treatments had the highest (5255.3 kgha-1) and the lowest (4055.1 kgha-1) grain yield, respectively. Among cultivars, Neda had the highest grain yield (5419.6 kgha-1). Cutting of 1/3 end of panicle and cutting of flag leaf treatments had the highest (88.55 %) and the lowest (76.4 %) panicle fertility, respectively. There were positive and significant correlations between grain yield and harvest index, panicle length and grain number per panicle, but 1000 grain weight had a negative correlation with grain yield that was not significant. Generally, results showed that cultivar Tarom had sink limitation and other cultivars (Neda, Shafagh and Fajr) had source limitation.

In order to study the source limitation and contribution of pre-anthesis assimilate to grain in dual-purpose (forage and grain) barley, a field experiment was carried out in Ahvaz region. The experiment design was split-plot in randomized complete block with tree replications. The application rates of N at four levels (60, 120, 180 and 220 KgN.ha-1) were main-plots. Sub-plots were three harvesting levels (Not cutting crop and cutting at five and 10 cm up to earth). Spikelet removal from one side of spike was used to determine source limitation. The results indicated that forage removal from five and 10 cm up to earth reduced grain yield 32% and 15.8%, respectively. The highest grain yield (530 g. m-2) was in 120 KgN.ha-1 treatment. Source limitation increased with harvesting treatment 28% and 23% in cutting the crop from five and 10, respectively. Generally, results shows grain yield reduced with increasing source limitation in dual-purpose barley. In cutting treatments, minimum source limitation was obtained with 270 KgN.ha-1.Dry matter translocation and the contribution of preanthesis assimilate to grain were effected by forage removal treatments.

In order to study the effect of limitation of source and sink on yield and yield components of cumin, an experiment was conducted in complete randomized block design in Research Field of Agriculture Faculty of Ferdowsi University of Mashhad during the years 2006-2007. The treatments were control, defoliation of 100% of leaves, defoliation of 50% of leaves and removing of 50% of umbrellas. The result indicated that in first sampling (10 days after treatments), dry matter and green area of plant significantly influenced by removing of leaves and umbrellas, in a way that increasing in defoliation cause reduction of dry matter accumulation and total green area of plant. In second sampling (24 days after treatments) defoliation of leaves and umbrellas imposed a significant effect on dry matter and total green area of plant. Leaf weight, stem weight and reproductive organs weight influenced by defoliation and umbrellas removing and in each three component the highest amount was observed in control treatment. In maturity stage, only the number of umbrellas per plant influenced by defoliation and umbrellas treatments. In control and defoliation of 50% of umbrellas, there was no significant difference between grain yield and biological yield. The highest grain weight and harvest index obtained at control and removing 50% of umbrellas. The lowest grain yield observed in 50% of umbrellas removing, whereas, the lowest biological yield observed in 100% defoliation. Moreover, the results indicated that when plant exposed with complete defoliation, accumulates more dry matter in reproductive organs and when exposed with half of umbrellas removing, dry matter partitioning pattern shift to vegetative organs.

To study the effects of plant density and source limitation on grain yield, yield components and dry matter and nitrogen remobilization in corn (Zea mays L.), a field experiment was conducted at Seed and Plant Improvement Institute in 1998. A strip plot design based on randomaized complete blocks with 4 replications was used. In this study maize hybrids (KSC704 and KSC711) were sown in vertical plots. Density (65, 70, 75, 80, 85, 90 thousand plant ha-1) and topping levels, T1 (control) and T2 (Removing tassel and all leaves above the ear) were assigned as factorial to horizontal plots. Results revealed that toppng at two weeks after anthesis did not have any adverse effect on grain yield. Therefore, a considerable quantity of forage could be harvested without any reduction in grain yield. The highest yield of green fodder (5.45 tha-1) was obtained from 90 thousand plant ha-1. Although topping caused an increase in 1000 kernel weight by 7 percent compared to control, but there was no significant difference in their grain yield. Remobilization of dry matter and nitrogen from different parts of th shoot (leaves and stem) to the grain responded differently and among them stem contributed more. Maximum remobilization of dry matter from stem (58%) was recorded in 80 thousand . plant ha-1 which had significantand positive correlation with grain yield.

In this study the effects of source limitation on grain yield of twelve barley cultivars (Aras’,‘Jonub’,‘Reihan’,‘Zarjou’,‘Sararoud’,‘Sahra’,‘Fajr30’,‘Karoun’,‘Gorgan’,‘Makouei ’and ‘Nosrat’) under post anthesis water deficiency were studied. Source limitation treatments were included that control, removing of awn, leaves below flag leaf, flag leaf and spike photosynthesis. All source limitation treatments significantly reduced grain yield, 1000 grain weight and number of grains per spike. In non-water stress, the highest reduction of grain yield was seen in removing of leaves below flag leaf treatment (27.6%). In water deficiency, the highest and the lowest grain yield reduction were seen in removing of spike photosynthesis (32%) and removing of awn (18.1%). Flag leaf removing significantly increased photosynthesis rate in remaining leaves in non-water stress (28.8%) and water deficiency (10.8%). The evidence from this study suggests that under water deficiency after anthesis, spike photosynthesis is more important than the other current photosynthesis organs in grain yield formation in barley.

Grain weight is regarded as one of the important factors on wheat genotypes, on the other hand this factor is related to the provided assimilates (or sources), especially in first stages of growth, and too it’s dependent to the capacity and capability of growing grains (sinks) in storing assimilates. Allocating higher level of assimilates to the economical sources or grains is one of the efficient way to achieve a high proceed in wheat genotypes. To investigate the effect of source restriction on qualitative features of five bread wheat cultivars (Kavir, Navid, Alvand, Norstar, gaspard) containing different growth habit (spring, facultative and winter) an experiment at the 1390-91. Cropping cycle strip split plot (Plot receiver band split in the number of treatments and resource constraints) based on randomised completely block design (RCBD) with three replications implemented on agricultural research station of West Islamabad in Kermanshah. The evaluated traits were thousand kernel weight, grain crude protein percentage in grains, grain starch and grain crude fiber, number of grains and their weight on spikes and the proceed. Analysis of variances and comparison of means using Duncan's Multiple Range Test (5%) ascertain that the resources constraints generate a meaningful influence on decrement of cultivars’ proceed. Also, cultivars have significant differences with each other according to their proceeding. While the most proceeding correspond to the Gaspard the least proceeding was seen in the Norstar. Furthermore, Results show that the cultivars have significant differences regarding to the number of grains per spike and their weights. Seems that the winter cultivars have a high level of crude protein and low level of starch due to their growth delay in ripening. However, the source constraints caused the decrease of many evaluated factors.