Selection Index for Seedling Root Traits to Improve Frost Tolerance in Winter Faba Bean

Mini Research

Ann Agric Crop Sci. 2016; 1(3): 1014.

Selection Index for Seedling Root Traits to Improve Frost Tolerance in Winter Faba Bean

Sallam A1,2* and Yasser Moursi³

¹Department of Genetics, Assiut University, Egypt

²Department of Agronomy & Horticulture, University of Nebraska-Lincoln, USA.

³Department of Biology, University of Fayoum, Egypt

*Corresponding author: Ahmed Sallam, Department of Genetics, Assiut University, Egypt

Received: October 21, 2016; Accepted: December 02, 2016; Published: December 06, 2016

Abstract

Frost stress causes a significant damage to winter faba bean yield. Root traits of faba bean seedlings play an important role in resistance to frost tolerance. The main objective was to study the genetic variation in root traits of faba bean seedlings after frost stress. A set of 208 diverse genotypes was tested. The experiments were conducted in a Frost Growth Chamber (FGCh). Root frost susceptibility (RFS), root fresh matter (RFM), and root dry matter (RDM) were scored on all plants after frost stress. A selection index was calculated to improve RFS using RDM and RFM. The results revealed a high genetic variation was found between all genotypes for all traits scored. The repeatability estimates was ranged from 0.52 (RDM) to 0.60 (RFM). Such a high genetic variation and repeatability estimated could be used for selection to improve frost tolerance in winter faba bean through breeding programs.

Keywords: Faba bean, Frost tolerance, Roots, Selection index

Introduction

Faba bean (Viciafaba L.) is one of the most important grain legumes due to its high protein content. The insufficient winter-hardy faba bean genotypes and winter kill in Europe force the spring type of faba bean to be sown [1]. Winter faba bean is higher yielding than spring type [2]. Therefore, breeding for improving frost tolerance in winter faba bean is needed [3]. Frost tolerance can be assessed in field experiments and controlled growth chamber. The advantage of conducting experiments in growth chambers is the ability to test and evaluate seedlings of many genotypes in a short time and thus develop suitable resistant cultivars [4]. Several methods and tools have been developed to study frost tolerance. Examples include visual scoring of freezing injuries in leaves under controlled conditions [5], loss of turgidity and loss of color of both leaves and stems [6]. Most of earlier studies assessed the effect of frost stress on shoots of faba bean [1,6-8]. The effect of the frost stress on roots of faba bean should also be taken into account due to the vital role of roots after exposing the plants to frost stress.

The objectives of this study were

1) to study the genetic variation in roots traits in faba bean seedlings.

2) to create a selection index for root traits in order to select the best frost tolerant genotypes.

Material and Methods

The plant materials consisted of 208 highly homozygous lines from Gottingen Winter Bean Population (GWBP) [9]. When the seedlings of GWBP reached to two expanded leaves, all plants were transferred to a Frost Growth Chamber (FGCh). The genotypes were sown in pots with soil and sand with 3:1, respectively. The experimental layout was alpha lattice design. The genotypes were evaluated in four experiments with two replications each (r = 8). All genotypes were exposed to a hardening phase for 10 days on 5°C, and then subjected to frost treatment three nights at -16°, -18°, and -19°C. The irrigation in the FGCh was applied to the keep the pots at approximately 70% of soil water capacity. The plants were irrigated during hardening phase and stopped when frost test started. After the frost test, the roots of each genotypes were carefully removed from the soil and cleaned with water. Root frost susceptibilit (RFS) was scored using a scale ranging from 1 (no frost symptoms) to 9 (black and dead roots) (Figure 1). Then Root mresh matter (RFM) was weighted for each genotypes. The fresh roots were dried for 48h at 55°C and weighted to estimate Root dry matter (RDM). A selection index was calculated as described in [10]. A root index (RI) was used to better describe RFS (X1) using two auxiliary traits RFM (X2) and RDM (X3) as: