Optimizing phenotyping methods to evaluate lodging risk for wheat

Lodging is a complex phenomenon affecting wheat production worldwide and is a consequence of the interaction of wheat plants with abiotic (wind, rain, etc.) and biotic (e. g. plant disease, etc.) factors. Wheat breeders rely heavily on incidences of natural lodging to select lines with resistance; however, the intermittent nature of lodging events means this approach is unreliable. A model of the lodging process has been published to estimate the lodging susceptibility of plants that uses information from 15 stem and root characteristics of field grown plants that influence lodging. This approach estimates lodging susceptibility in the absence of natural lodging. However, the main shortcoming of this methodology for plant breeders is the amount of time required to measure these traits (100-150 min per plot). This study investigated two strategies to optimise the methods of estimating lodging risk in the absence of natural lodging: i) determining the minimum number of plants that must be measured per experimental plot (sample size) to identify genetic differences and ii) minimizing the number of traits required to assess lodging susceptibility increasing the feasibility to apply the methodology in a breeding context. Spring wheat grown under North West Mexico environmental conditions was established during four crop seasons (2010 - 11, 2011 - 12, 2012 - 13 and 2013 -14) for this study. Results indicated an optimum sample size of seven plants per plot as the minimum required to identify genetic differences between cultivars with good statistical power and precision (assuming each treatment plot was replicated 3 times). Cultivar ranking and absolute values for trait dimensions were maintained when compared with larger sample sizes. A reduced number of traits can be used to estimate cultivar lodging susceptibility performances and key traits include: plant height, ear number per plant, ear area, natural frequency, breaking strength, length, diameter and wall width of one basal internode, structural rooting depth and root plate spread. Targeting these key traits, this study established that on a daily basis, 10 (47 min per plot) plots can be assessed by measuring seven plants per plot per person. Moreover, if the screening focuses only on the key traits for leverage/stem/root dimensions, then the daily plot assessment capacity would increase to 25.