Factors Affecting the Incidence of Pod Anomaly Disorder and Seed Yield of Soybean [Glycine max (L.) Merrill] in Golestan Province in Iran

Over the past four decades, pod anormaly disorder has been one of the most important factors affecting soybean seed yield and production in Golestan province in Iran. To assess the role of crop management factors on soybean pod anormaly and seed yield, 80 soybean fields were selected randomly during 2018 and 2019 in Gorgan and Aliabad in Glestan province. Stepwise regression analysis showed that seed yield model (Yield = -442.5 + 6.9 X1 + 180.2 X2 + 866.2 X3) was determined with three factors of potassium fertilizer (X1), number of irrigation (X2) and insect pest management (X3). Potassium fertilizer, number of irrigation and insect pest management explained 19.2%, 18.7% and 62.1% of the yield gap components, respectively, and reflected the importance of these factors for increasing soybean seed yield. Among 80 soybean fields, 15 and 18 fields had full and partial pod anomaly disorder symptoms, respectively. The mean soybean seed yield for fields without and partial pod anomaly disorder was 3039 and 848 kg ha-1, respectively. The results of this study showed the importance of optimum insect pest management to prevent and control the incidence of soybean pod anomaly disorder in Goletan province in Iran.

Over the past four decades, pod anomaly disorder has been one of the most important factors affecting soybean seed yield and production in Golestan province in Iran (Payghamzadeh, 2017; Malek Shahkouei et al., 2019; Faraji et al., 2023). This conditions has led to disorders in the flower and pod system of the soybean plant which ultimately causes no or low pod set, modified of pods shape, stay-green plants, and so called by the farmers, fodder plants In fact, in the affected plants, a mechanism prevents the transfer of assimilates from leaves to seeds, hence the leaves remain green and the plants continue vegetative growth. In 2015, about 13765 hectares out of the total of 35107 hectares (about 39% of the soybean growing areas) suffered from this disorder. Due to luck of adequate quantitative information on the role of each of the factors in the incidence of this disorder and seed yield reduction, it would be necessary to investigate the effect of each of these factors on reduction of the soybean seed yield to enable farmers to overcome these limiting disorders by adopting appropriate crop management strategies.
 

In order to investigate the role of management factors affecting the seed yield and incidence of pod abnormality disorder in soybean, during the years 2018 and 2019, 80 soybean fields in the two cities of Gorgan and Aliabad, were determined and investigated. These fields included good, medium and poor fields and even seed production ones. Soybean variety cultivated in all investigated fields was Katul. During the growing season, the stages of development, including the date of planting, emergence, beginning and end of flowering, podding, seed filling, physiological maturity and harvest maturity were determined (Fehr et al., 1971). For data analysis, the collected information was normalized (SAS, 1997). To determine the yield model, qualitative variables were coded as zero and one. Then, the relationship between all quantitative and qualitative measured variables with yield was investigated through step wise regression method and data analysis was performed using the statistical method of yield comparison analysis (Soltani et al., 2009). Finally, using the yield model and parameter values, potential yield, yield gap and the contribution of each factor causing the yield gap were determined.
 

Out of 80 studied soybean fields, 47 fields had completely normal soybean plants and no pod anomaly disorder, 18 fields had moderate pod anomly disorder and 15 fields had completely affected by pod anomaly disorder. Mean seed yield in fields without disorder, with moderate disorder and complete disorder was 3039, 848 and 0 kg ha-1, respectively, indicating considerable sedd yield reduction of 72% and 100% in fields with moderate and complete disorder in comparison with fields without disorder. These results reflected the importance of pod anomaly disorder in reducing soybean seed yield. The seed yield model estimated the average and maximum seed yields as 2003 and 4792 kg ha-1, respectively. The estimated yield gap was 2789 kg ha-1 that with approperiate crop management particularly effective insect pest control, adequate potassium fertilizers application and adequate number of irrigations can be narrowed and even closed. The results of this two-year field study showed that under the conditions of Golestan province, it is possible to significantly increase soybean seed yield by application and adoption of appropriate crop management startegies and techniques.