Investigation the Physiological Traits Associated with Canola (Brassica napus L.) Genotypes Yield Improvement

Canola (Brassica napus L.) is one of the most important oil crops in the world. It has placed in third rank after soybean and palm and has the fastest of growth rate among oil seed in recent decades too. Canola yield was 1592 and 1567 kg.ha-1 in Iran and the world in 2003, respectively, however it has increased to 2125 and 2043 kg.ha-1 in Iran and the world in 2014, respectively. Crop physiologist should investigate the important physiological parameters which in the past have increased yield and can help to increase the quality and quantity of crop yield in the future. Therefore, the current study was carried out to evaluate the physiological traits associated with canola (Brassica napus L.) genotypes yield improvement. Experiment was conducted as randomized complete block design with four replications at Higher Education Complex of Shirvan during growing seasons 2014-2015 and 2015-2016. Treatments were included 20 cultivars and lines of rapeseed. The record of phonological stages was done based on Sylvester-Bradley (1984)’s method. Before the plants showed elongation. Aboveground biomass and leaf area index (LAI) were measured from destructive sampling and it has been continuing at intervals of 6 to 10 d until physiological maturity. The ratio intercepted photosynthetic active radiation (PAR) was obtained by measuring of radiation at the top and bottom of the canopy with a Ceptometer (ACCUPAR model LP-80). Light was measured just before each destructive sampling between the hours of 12 to 14 on clear days. To calculate the daily cumulative solar active radiation we used RLY- calc program (Soltani, 2011). In order to investigation of growth indices, we have divided the varieties to three group based on cluster analysis and is select a variety as group representative. The groups are included high yield (Bilbao), medium yield (Karaje 3) and low yield (Sarigol). Results indicated that there were significant differences among studied varieties in terms of phenological traits. So that Sarigol, Talayee, Shirali, Zafar and Zarfam were achieved earlier than others to physiological maturity. Positive and significant correlation of flowering duration with yield and the number of pod plant-1 has showed its importance in determination of yield. Positive and significant correlation among flowering duration with yield (r=0.66**) and the number of pod per plant (r=0.88**) showed its importance in determination of yield. Also, the most important of stage at making yield was affected by environmental conditions such as temperature, radiation and rainfall. LAI for Bilbao was higher than Sarigol and Karaje 3. Also, Sarigol was achieved maximum LAI earlier than two other varieties. There was strong correlation between yield and maximum dry matter accumulation (r=0.81**). The synchronization of maximum LAI with more solar radiation was much more important to achieve maximum yield. In the first year of experiment, crop growth rate (CGR) and relative growth rate (RGR) were higher than second. There was more solar radiation in first year that it was increased growth indices. The average extinction coefficient of light (KPAR) is estimated 0.70 and 0.72 in the first and second year of experiment respectively. In the first year of experiment, KPAR was varied between 0.65 (Shirali) to 0.76 (Modena and GKH-2005). In the second year, the highest and lowest extinction coefficient was belonged to the varieties Zafar (0.80) and Karaje 3 (0.63) respectively. The average of radiation use efficiency (RUE) is estimated between 3.8 and 3.6g MJ .m-2 in the first and second year respectively. Reducing light use efficiency in the second year can be probably because of obvious difference of weather between two years especially decreased of radiation. In other words, more scattered radiation in the second year than first year can be a major reason for this difference. In general, grain yield in the first was more than the second year of the experiment. The average yield of cultivars in the first and second year was 453.8 g.m-2 and 401.8 g.m-2 respectively. The highest yield in the first year belonged for Bilbao, Kodiak, SW102, GKH-305 and Traviata with the mean 495.5 g.m-2 and the lowest yield related to Zarfam, Sarigol, Talaei, Shiraly and Modena with the average amount of 370.5 g.m-2. The highest yield in the second year belonged to Bilbao, GKH-305, Slm046, L72, SW102, Kodiak and Traviata with the average amount of 450.3 g.m-2 and the lowest yield belonged to cultivars Talayeh, Opera, Karaj 3, Okapi, Modena, GKH-2005 and Karaj 1 with an average yield of 349.7 g.m-2. In general, cultivars with a higher LAI, as well as whose their maximum LAI coincided with higher radiation input had higher yield. It can be concluded the importance of the synchronization maximum leaf area index with more solar radiation. For canola if the maximum LAI is less than four can say that growth and yield will be limited due to lack of leaf area because LAI about four is sufficient to obtain about 90 % of solar radiation. Therefore in spite of second year, in the first year LAI was not limiting factor to achieve maximum biomass. Since maximum LAI of canola occurs in flowering stage, so higher leaf area index at this time was caused the cultivars use more solar radiation. In addition to maximum LAI, the coincidence maximum LAI with higher radiation input was important factor to achieve a higher yield as a result more dry matter accumulation.