Abstract: In order to evaluate plant density and cultivar effects on grain filling rate and duration, yield and its components of 3 pinto bean cultivars a factorial experiment (using RCB design) was conducted in 2007 at agricultural and natural resources research institute in East Azerbaijan province (Tabriz/Iran). Three cultivars (Khomeyn, G -14088 and 11816) were planted at 4 densities (14, 20, 30 and 60 plants m^-2) in 3 replications. A 2-part linear model was used to quantifying the grain filling parameters. Interaction effect of cultivar and plant density affected Grain Filling Rate (GFR), Mass Maturity (MM), Maximum Grain Weight (MGW) and Effective grain Filling Period (EFP) significantly. Highest amount of these parameters observed at Khomeyn cultivar in 14 plants m^-2. These parameters decreased in Khomeyn and G-14088 cultivars with increasing in plant density significantly. Between cultivars and plant densities treatments of pinto bean was significant difference in yield and its components. But interaction effect of cultivar and plant density affected only days to maturity, number of pod per plant, 100 seed weight and grain yield parameters. These parameters (except grain yield) decreased with increasing in plant density. But increasing of plant density and number of pod in square meter compensated reduction of yield components. Therefore, grain yield increased with increasing in plant density. Khomeyn cultivar had maximum amount GFR, MGW, EFP, number of pod per plant, 100 seed weight and grain yield. Therefore, Khomeyn and 30 plants m^-2 are best cultivar and plant density in pinto bean, respectively.

INTRODUCTION

Beans are from primitive crops of new world and also they contain half legumes used by mankind in the world (Broughton et al., 2003). Plant density is one of important and effective factors in determining of crop yield. Plant density isn’t constant for one cultivar in different climatic conditions. In optimum plant density, inside and outside competition of shrubs should be minimal and enough space should exist for crop culture. The first studies were conducted by Kakiuchi and Kobata (2004), who observed that lower plant density increased the pod number per plant and higher plant density decreased the pod number per plant. Maddonni et al. (2006) observed that the highest 100 seed weight (41.13 g) is obtained in 30 plants m^-2 and the lowest 100 seed weight (37.59 g) is obtained in 50 plants m^-2 in kidney bean. Bruin and Pedersen (2008) observed that soybean planted in 38 cm row spacing yielded 248 kg ha^-1 greater than soybean planted in 76 cm rows. Gan et al. (2007) have also shown increase of grain yield at higher plant density in chickpea. Wang et al. (1997) showed that in high plant density cultivars maturity occur earlier than low plant density so that plant maturity in 60 plants m^-2 was 10.18 and 4.13 days earlier than 30 and 40 plants m^-2. Grain filling rate and grain filling duration are tow important traits in determining of grain yield that by means of them we can explain grain yield changes. Grain filling period from fertilization to grain maturity stage can be separated into 3 stages: in 1st stage, grain weight increase slowly in the course of lag phase, in 2nd stage, linear stage of grain filling starts and 90% of increasing of grain dry weight is in 2nd stage. The 2nd stage is named effective grain filling period. In 3rd stage that is named maturity stage, grain dry weight doesn't have noteworthy increase and the relation of mother plant with seed is interrupted at the end of 3rd stage. The growth and development of seed that harvested for commercial yield in grain crop contains 2 part: one part is grain filling rate and another part is effective grain filling period. GFR is collection of dry matter in ratio time (day) at linear stage of grain filling. Grain filling rate is estimated by linear regression that is obtained from grain dry weight at several times in the course of grain development and after omission of non-linear data. Determining of grain filling duration is very difficult because assignment of exact time of beginning and ending of grain filling is impossible.

We can use fertilization and grain formation for grain filling beginning and physiological maturity for ending of grain development (Royo et al., 2007). Effective grain filling period is obtained by ratio of grain yield to grain filling rate in the course of linear stage of grain filling (Broughton et al., 2003). Wang et al. (1997) reported grain filling rate and effective grain filling period decrease with increase in plant density significantly in wheat. Bruin and Pedersen (2008) have shown decreasing of grain filling rate, mass maturity, effective grain filling period and maximum grain weight in indeterminate cultivars of soybean but he reported that grain filling rate increase in determinate cultivar of soybean with increase in plant density. In this study, we tried to show effects of different cultivars and plant densities on grain filling parameters, yield and its components, explain of grain yield changes by grain filling parameters and also we will introduce the best cultivar and plant density of pinto bean that has the highest grain yield.

MATERIALS AND METHODS

A factorial experiment (using RCB design) was conducted at East Azerbaijan province (Tabriz/Iran). On 29th April, 2007 3 cultivars (Khomeyn, G -14088 and 11816) were planted at 4 densities (14, 20, 30 and 60 plants m^-2) in 3 replications. For assessment of increasing procedure of grain dry weight in the course of grain filling duration, sampling from seeds started 20 days after flowering and continued in 9 times in 6 days intervals. A linear regression model (2 parts) was used in order to estimate and analyze of grain filling parameters:

(1)

In Eq. 1, GW is grain weight, a is width of beginning in line, t is degree days after pod formation or days after flowering and t _max is mass maturity time. This model separates grain weight changes in relation to time into two stages: In 1st stage (linear stage of grain filling), grain weight increase until arrive to maximum rate (mass maturity). The slope of regression line in this stage (a) indicates grain filling rate. In 2nd stage grain dry weight doesn't have any changes and its changes become constant. By means of this model, grain filling rate and mass maturity are obtained and then for estimate of maximum grain weight, the data of mass maturity was put in second part of Eq. 1. After calculation of grain filling parameters by means of DUD method and Proc NLIN order in SAS software that is applicable method of linear regression model (2 part) in computer, all data were analyzed using a factorial experiment (using R.C.B design) by means of SAS software. Treatment means were separated using Tukey's Test at 0.05 statically level.

RESULTS AND DISCUSSION

Application of Eq. 1 for grain dry weight data indicated same pattern for seed development in all of densities. Grain dry weight of cultivars had initially linear increase at 4 densities. Then increasing of grain dry weight arrived to maximum rate (mass maturity or physiological maturity). After this point grain dry weight didn't have any changes and its curved line became a horizontal and directive line. Cultivars had different grain filling rate in 4 densities (Table 1). Maximum rate of GFR was obtained at Khomeyn and 14 plants m^-2 (least density) that its amount was 6.694 mg day^-1. GFR of G -14088 decreased with increase of plant density (Table 2). These cultivars have indeterminate growth therefore, they produce a lot of branches per plant and too much absorbed nutrient consume for vegetative growth in higher plant densities. Consequently the portion of seed from absorbed nutrients will be fewer and grain weight decrease. Because GFR is obtained by ratio of maximum grain weight to EFP therefore, GFR decreased with grain weight decreasing. The 11816 has determinate growth and produces few branches in main stem in lower plant densities in comparison with indeterminate cultivars. The amount of GFR in higher densities was obtained more than lower densities at 11816 (Table 2). The time of mass maturity was found to be significantly different for cultivars at all of plant densities (Table 1). Mass maturity time of cultivars ranged from 49.07-64.63 days. MM were 4 and 10 days later in lowest density of Khomeyn and G-14088, respectively in comparison with highest density (Table 2). Reason of MM reduction with plant density increasing can be fewer branch production per plant in high plant density and formation of pods at the top of plant that result in earlier maturity of grain and short time

Table 1:	Mean squares from analysis of variance of grain filling parameters in pinto bean
*, ** = significant at 0.05 and 0.01 statically levels, respectively

Table 2:	Mean comparison of grain filling parameters in different densities of pinto bean cultivars
Different characters in per column indicate significant difference at 0.05 statically levels. A1 = Khomeyn; A2 = G-14088, A3 = 11816. D1 = 14p/m2, D2 = 20 p m-2, D3 = 30 p m-2 and D4 = 60 p m-2

for mass maturity. Highest amount of effective grain filling period was seen at Khomeyn and 14 plants m^-2. EFP was not affected by different plant densities in G-14088 and 11816 (Table 2). Because of flower formation at the lower parts of plant stem and being longer days to maturity (because of many pod per plant) in lower density, EFP lasted a long time. Wang et al. (1997) showed similar results in wheat. Greatest rate of maximum grain weight was obtained of Khomeyn in lowest density and least MGW was obtained of G-14088 in highest density. Maddonni et al. (2006) showed that an increase in plant population density reduced kernel weight. But in 11816 highest rate of MGW was obtained at highest density (Table 2). Bruin and Pedersen (2008) obtained similar results in determinate cultivar of soybean so that an increase in plant density from 30-40 and 50 plants m^-2 resulted in MGW increase from 80.67-89 and 89.33 g. Lower densities of Khomeyn and G-14088 had higher GFR and EFP and because MGW is calculated of GFR and EFP by this formula: MGW = EFPxGFR consequently maximum rate of MGW was obtained in least density in these cultivars. But in 11816 maximum rate of GFR, EFP and MGW were obtained in highest density.

Between cultivars and plant densities of pinto bean was significant difference in yield and all of yield components. But interaction effect of them affected days to maturity, number of pod per plant, 100 seed weight and grain yield (Table 3).

Highest and lowest days to maturity were obtained at Khomeyn in 14 and 60 plants m^-2, respectively (Table 4).

Table 3:	Mean squares from analysis of variance of data for yield and yield component traits in pinto bean
** = significant at 0.05 and 0.01 statically levels, respectively

Table 4:	Mean comparison of yield and yield components traits in pinto bean cultivars
Different characters in per row indicate significant difference at 0.05 statically levels. A1 = Khomeyn, A2 = G-14088, A3 = 11816. D1 = 14 p m-2, D2 = 20 p m-2, D3 = 30 p m-2 and D4 = 60 p m-2

In higher plant density fewer branch per plant and appropriation of great photosynthetic materials for main stem result in reduction of days to flowering and maturity. Wang et al. (1997) showed similar results. Number of pod per plant decreased with increasing of plant density in three cultivars because of competition for nutrient, slight and space for growth (Table 4). Kakiuchi and Kobata (2004) observed similar results. Maximum rate of 100 seed weight was seen at Khomeyn and in lowest plant density. Minimum rate of 100 seed weight was seen at G-14088 and in highest plant density (Table 4). With due attention to decrease of GFR, EFP and particularly MGW in higher plant density reduction of this parameter was reasonable. Royo et al. (2007) indicated that highest 100 seed weight (160.7 g) was obtained in 30 plants m^-2 and lowest 100 seed weight (102.2 g) was obtained in 50 plants m^-2. Although, all parameters decreased with increasing in plant density, not only grain yield didn’t reduce with increase of plant density but also increased in all cultivars. But this increasing was continued to 30 plants m^-2 (optimum plant density) and then grain yield decreased in 60 plants m^-2 (Table 4). Reason of grain yield increase can be increasing of number of plant and pod number in square meter that compensated decreasing of yield components. Norsworthy and Shipe (2005) reported that seed yield was 211 g m^-2 in narrow rows compared with 107 g m^-2 in wide row.