The relationship between leaf area and vegetative characteristics in Barecat and French faba bean cultivars

Introduction Since the leaves are the main source of production of photosynthetic substances in plants, dry matter production and crop yield potential is largely depend on the leaf surface, and many environmental changes affect growth and yield through changes in leaf area. Hence, green leaf area per plant and leaf area index measure in almost all studies of crop physiology to understand the mechanism of yield alteration. However, measurement of leaf area compared with other traits such as plant height and total plant dry weight is very difficult, precise instruments and spend more time and cost. Therefore, according to the allometric relationships in plants, extensive studies were done to find the relationship between leaf area and other plant traits that their measurement is easier, faster and cheaper, and does not require expensive equipment. Allometric relationships in plants reveal changes in the growth of an organ of plant than to all or another part or organ of plant. The leaf area in plant as main source of photosynthetic substances closely associated with the growth and yield. Thus, it is usually measured for justifying variations of the growth and yield. Due to the difficulty, time‌consuming and requires devices to measure leaf area, an alternative approach for measuring the leaf area is the use of allometric relationships between leaf area and traits that their measuring is easy and quick and requires no expensive equipment. This study aimed to obtain the allometric relationships between green leaf area and a number of vegetative attributes such as number of leaves per main stem, green leaf dry weight, total dry weight of vegetative parts of plant. Allometric equations was used successfully to calculate leaf area in various crops such as cotton, wheat, chickpea, faba bean, peanuts, soybean and sweet sorghum. The effects of three factors cultivar, inter‌ and intra‌row spacing on the allometric relationships were examined.   Materials & Methods This experiment was conducted using two cultivars of faba bean (a conventional, Barecat and a new cultivar, French), three inter‌row spacing (25, 50 and 75 cm) and two intra‌row spacing (8 and 15 inches) in a randomized complete block design with 4 replications in the farm of Gorgan University of Agricultural Sciences and Natural Resources during 2010‌2011 growing season. Sampling to measure the green leaf area and leaf dry weight and other vegetative traits during the growing season was carried out with intervals of 7 to 15 days (depending on the temperature and rate of plant growth). Different mathematical functions were fitted to the data to obtain allometric relationships. To compare the accuracy of the equations, coefficient of determination (R2) and root mean square error (RMSE) were used. Higher coefficient of determination, and lower coefficient of variation and root mean square error reflects the higher accuracy of the equation to describe allometric relationships.   Results & Discussion According to the results of this experiment, the relationship between leaf area and leaf dry weight and total plant dry weight in faba bean was not affected by cultivar, inter‌ and intra‌row spacing, statistically. Thus, an equation was fitted to leaf area data against leaf dry weight or total plant dry weight in all treatment (both cultivars and all inter‌ and intra‌row spacing). Also, results of this study showed that the relationship between green leaf area and leaf dry weight as well as number of nodes per main stem has higher coefficient of determination (0.98 for green leaf dry weight, and 0.98 and 0.95 for node number per main stem in 8 and 15 cm intra‌row spacing, respectively) and lower the root mean square (1.05 for green leaf dry weight, and 1.08 and 1.064 for node number per main stem in 8 and 15 cm intra‌row spacing, respectively) than other traits.   Conclusion Since the relationship between green leaf area and green leaf dry weight per plant had a higher coefficient of determination (0.98) as well as smaller root mean square (1.05) than other traits including leaf number per main stem, as well as the ease of measuring the green leaf dry weight, it is suggested that the relationship between leaf area and leaf dry weight (a segmented relationship) is used to estimate green leaf area during the growing season in faba bean. Also, this relationship can be used to predict faba bean leaf area with sufficient accuracy in the simulation models.