HARVEST INDEX (HI), ratio of seed yield to aboveground dry matter, is a very important parameter for estimating seed yield in several crop models. In this study, the importance, definition, variability and estimation methods of HI in crop models were discussed. HI estimation methods are categorized into two groups including: (i) complex methods that estimate HI from the beginning of seed growth to crop maturity, dynamically and (ii) simple methods that estimate the final HI at crop maturity. HI is a trait that is affected by many environmental parameters and the genotype of a crop. Soil water content or soil water suction during growing season, soil nutrient, groundwater depth, high air temperature, plant population and irrigation water salinity are some environmental factors affecting the HI. Therefore, in all models that used HI to estimate crop yield, either complex (e. g., AquaCrop model) or simple method, the HARVEST INDEX estimating equations should be calibrated by changing the genotypes or cultivars, environmental and non-environmental parameters.

HARVEST INDEX is one of the important parameters in estimation of modules of seed yield prediction. Since, this parameter undergoes changes under various conditions. Therefore, this research was aimed to prepare relations to estimate it. for this purpuse, a compound analysis experiment with randomized complete block design with four replications was conducted at the Gorgan University of Agricultural Sciences and Natural Resources Univercity Research Farm in 2005. The treatments were four wheat varieties (Koohdasht, Shirudi, Tajan, Zagros) and six different sowing dates (14 December, 20 Jan, 20 Feb, 20 March, 16 Apr, 17 May). The results indicated that a significant difference was obvious in different sawing dates in respect to the slope of HARVEST INDEX line (dHI/dt). These changes were attributed to mean temperature, pre-Grain filling accumulated biomass, and fraction of post-anthesis (fG) producted dry matter. Therefore, based on obtained results and evaluated models, fG was the best optian for simulation of dHI/dt and HARVEST INDEX, in this respect, RMSE of dHI/dt for all varities by fG was 0.25 percentage per day which was the lowest one. Therefore, these relations can be used to evaluate the slope of HARVEST INDEX line, or to model grain yield in crop simulation models.

Pre-HARVEST sprouting is one of the main factors that reducing the rice grain yield and quality in humid weather condition with raining at HARVEST time. Thirty four local and improved rice cultivars were evaluated for pre-HARVEST sprouting and some related characteristics to this trait at in vivo condition. Analysis of variance results indicated that the differences between rice genotypes were significant for pre-HARVEST sprouting and some other traits of grain. Genotypic and phenotypic correlation coefficients of pre-HARVEST sprouting with alpha amylase activity were positive, this result showed that the alpha amylase activity had significant effect on pre-HARVEST sprouting. All rice cultivars classified into three groups by cluster analysis using ward method. First group included 24 cultivars and second and third groups included 4 and 6 cultivars respectively. In total, cultivars of the first and third groups had the lowest of pre-HARVEST sprouting rate, so they were resistant to germination before HARVEST and the cultivars of second group had the highest of pre-HARVEST sprouting rate, so they were sensitive to germination before HARVEST. Results of this experiment showed some local rice cultivars such as Domsefid and Hashemi, with high resistance to pre-HARVEST sprouting could potentially be used in breeding programms.

To evaluate the effect of different weeds interference periods on shoot and root growth and HARVEST INDEX of chickpea, an experiment was conducted at two environments using randomized compelete block design with four replications. Experiment environments were Tabriz and Kermanshah at first and second year, respectively. In each experiment, twelve treatments consisted of six initial weed-free periods (in which, plots were kept free of weeds for 0, 12, 24, 36, 48 and 60 days after crop emergence (DAE), and then weeds were allowed to grow until HARVEST) and six initial weed-infested periods (in which, weeds were allowed to grow for 0, 12, 24, 36, 48 and 60 DAE, after which the plots were kept free of weeds until HARVEST). The results indicated that, with increase of weed-infested and reduction of weed-free duration, the length and weight of chickpea shoots and roots significantly reduced as compared to control (weed free for all of the growing season). The reductions were more for roots than shoots. Consequently, shoot length: root length and shoot weight: root weight ratios increased. Moreover, reduction was more for weight of shoots and roots as compared to their length. HARVEST INDEX was also significantly decreased with increasing of weed-infested duration and decreasing of weed-free period. This reduction was 42.8% for full season weedy treatment as compared to control.

To study the response of bread wheat genotypes to drought stress in post-anthesis stage of drought resistant genotypes, this experiment was conducted with 18 kinds of bread wheat genotypes. The experiment was performed in a RBCD with 3 replications under normal and drought stress conditions during 2004- 2005 and 2005- 2006 cropping seasons in Karadj Agricultural Research Station. Combined analysis of grain yield showed that effect of time of the year, irrigation, genotype and interaction effect of genotype × year were significant. Only the effect of irrigation and genotype were significant in HARVEST INDEX. Using SSI and TOL genotype C-83-7 and using STI, MP and GMP genotype C-83-8 were determined as the most tolerant genotypes. Correlation coefficients of these indices with each other for indices such as MP, GMP and STI were significant. Because STI was correlated with MP, GMP, TOL and SSI indices and also differentiated the genotypes belonging to "A" group from other group effectively, therefore, it could be recommended as the most suitable INDEX for the selection of drought tolerance bread wheat genotypes.

Drought stress is one of the most important environmental stresses affecting plant growth, yield and crop production around the world. It is believed that arbuscular mycorrhizal fungi are used for protecting plants against drought damage. Vesicular-arbuscular mycorrhizal fungi have been used in recent years to cope with water stress in many plants. In this study, the relationship between water deficit stress and mycorrhizal fungi were analyzed with mycorrhizal dependence INDEX and chlorophyll stability in sesame (Sesamum indicum L. ). The experiment was conducted in a split-plot design based on randomized complete blocks with three replications in the research field of Agricultural Research Center, West-Azerbaijan during years 2015 and 2016. The main factors consisted of normal irrigation, moderate and severe water stress and subplots included two different species of mycorrhizal fungi namely, Funneliformis mosseae and Rhizophagus intraradices. A noninoculated plant served as the control. Mean comparison based on 2-years data showed that with increasing severity of water stress, biological water use efficiency (WUBE), oil HARVEST INDEX (OHI) and protein HARVEST INDEX (PHI) decreased. Using two kinds of mycorrhizal fungi F. mosseae, R. intraradices compared to non-inoculated, caused an increase in WUBE and PHI about 28 and 20% and 6 and 2%, respectively. Also in three different irrigation conditions, the effect of F. mosseae and R. intraradices was similar on chlorophyll b stability INDEX (CSIb). The maximum and minimum WUBE (0. 96 and 0. 43 kg/m3), OHI (17. 61 and 10. 03%) and PHI (9. 36 and 5. 80%) were obtained under optimal irrigation and severe drought stress conditions, respectively. The maximum (34. 69%) and minimum (20. 26%) of mycorrhizal dependence INDEX based on biological yield (MDIBY) were observed under severe drought stress and optimal irrigation conditions, respectively. Therefore, inoculation with mycorrhizal fungi (measured by MDIGY and MDIBY) under drought stress caused an increase in the chlorophyll (measured by TCSI). Increasing the chlorophyll led to an enhancement in the photosynthesis and promoted WUEE and WUBE. Improvement of the WUEE and WUBE caused an increase in oil and protein (measured by OHI and PHI). In severe and moderate water stresses mycorrhizal dependence INDEX based on grain yield (MDIGY) and MDIBY increased compared to optimal irrigation. It can be concluded that for achieving high WUEE, WUBE, OHI and PHI, TCSI and as a result tolerance to the water stress can be increased.

Soybean seed size is a key component of the crop performance and can affect the adaptation of the crop varieties to different environmental conditions and also affect the early vigor. To investigate the effect of seed size on yield, HARVEST INDEX, seed germination and seed vigor of soybean cultivars two experiments were conducted in the field (completely randomized blocks design, four replications) and at Seed Technology Laboratory  Islamic Azad University of Tabriz (completely randomized design, three replications)  in 2008. The treatments were cultivars at 2 levels (Williams and TMS) and seed size at three levels (small, medium and large). Results showed that increase in the seed size resulted in the seed yield and HARVEST INDEX increment. The maximum grain yield per unit area (with 518.5 kilograms per square meter) was observed in the large seeds of TMS cultivar, whereas, the lowest value (418.1 kilograms per square meter) was related to the small seeds of TMS cultivar. The large seeds HARVEST INDEX was 11.94% higher than small seeds. The laboratory results showed that germination percentage increased along with the increase in the seed size. The large seeds had 39.06 % higher germination compared to the than small ones, however, the effect of seed size on germination rate was not significant. The highest and lowest seedling lengths belonged to Williams' medium and small seeds, respectively.

To study the effect of drought stress on yield and grain yield components of clover, an experiment was conducted at the agricultural research station of Saatlo in Uremia during 2009-10. Experimental design was split plot, completely randomized block design with three replications. The main plots consisted of normal and stress irrigation treatments and the sub plots included 17 species and varieties of yearling clover. Clover genotypes in terms of traits such as spike weight per plant, seed number in plant, thousand grain weight, grain yield and HARVEST INDEX were studied on the farm. Results of the data review showed that the effect of varieties on all the traits were statistically significant at the 1% level. Irrigation factor on thousand grain weight was significant at the 1% level and on both traits spike weight, seed number per plant and grain yield were significant at the 5% level. The interaction of two factors irrigation in cultivars, on seed number per plant, were statistically significant at the 5% level, and on the spike per plant and grain yield traits, were statistically significant at the 1% level. Also, maximum grain yield was obtained for genotype No. 11 with normal irrigation (164.11 kg ha-1) and with drought stress (115.12 kg ha-1). The results of this study showed that genotypes 2 and 11, the T. Resupinatum can be introduced as high yield in genotypes in drought stress.

In order to study of different levels of zinc on yield, yield components and HARVEST INDEX in maize plant mycorrhiza under drought stress, an experiment was carried out in research farm of Arak Islamic Azad University in 2006. The experiment was laied out in factorial based on RCBD with three replications. The treatments were consisted as three levels of irrigations (irrigation equal of crop water requirementcv as control, irrigation equal of 75% crop water requirement and irrigation equal of 50% crop water requirement), inoculation with mycorrhiza fungi (Glumus intraradices) at two levels (inoculation with and without mycorrhiza) and zinc sulphate at three levels (0, 25 and 45 kg/ha). The result showed that, drought stress reduced HARVEST INDEX, yield and yield components significantly. Effects of mycorrhiza fungi on traits of number of grain per row, number of grain per ear, ear weight and grain yield was significant. Inoculation with mycorrhiza improved measured traits as compared to treatment of without mycorrhiza not only in condition of optimum irrigation but also drought stress. Using of mycorrhiza and zinc sulfate alone in condition irrigation control increased traits of measured. It was showded that with irrigation equal 75% water requirement, inoculation with mycorrhiza and 45 kg/ha zinc sulfate obtain optimum yield.