Evaluation of cold-tolerance in some annual forage crops genetic resources under cold conditions

IEvaluation of cold-tolerance in genetic resources of some annual forage crops under cold climatic conditions


Introduction

Temperature influences plant physiological processes, cellular structure and development. Habitat from which plants originate has undeniable effects on plant tolerance to cold temperatures. Plants from higher latitudes exhibit more tolerance to cold stress than plants from lower latitudes. When plants are exposed to cold stress, a sequence of events is triggered inside them, leading to an improved tolerance to the environmental condition. This phenomenon is known as plant hardening. Having access to winter-hardened species and cultivars is one of the important necessities for the development of crop production systems in local microclimates of cold regions. Utilizing genetic diversity in crop plant resources is an important approach towards achieving sustainable agriculture. Diversity in Iran`s forage germplasm for traits such as early maturity, high ratio of leaf to stem, dense ground cover and high yield has been shown in temperate regions such as Karaj and Mashhad (Abbasi, 2009, Abbasi et al., 2017). Testing a selection of these germplasm accessions can determine their potential for growing under water-limited conditions in cold regions. Hence, different genera and species of legumes in national plant gene bank of Iran originated from high latitudes were used to be evaluated under cold growing conditions.
Materials and Methods
A total of 124 annual-forage accessions from 40 species and 10 genera were selected based on the previous research works and were planted in an experimental filed at Jolge-Rokh agricultural research station. The number of accessions in each genus included Trifolium (36 accessions), annual medics (28 accessions), Onobrychis (9 accessions), Vicia (21 accessions), Melilotus (17 accessions), Lolium (6 accessions), Bromus (5 accessions), and Phalaris (1 accession), Lathyrus (1 accession) and barley (1 accession). Each accession was planted in two 2-meter long rows spaced 50 cm apart using an augmented experimental design. Some of the traits characterized in this study from autumn to spring included growth rate in spring and autumn, cold-tolerance score, plant height etc (IPIGRI, 1984). Statistical descriptive parameters were determined for the evaluated traits. One-way ANOVA (analysis of variance) and Duncan's multiple tests were performed on data of each trait. The analyses were carried out by SPSS 15.


Results and Discussion
Meteorological data showed that there were a total of 68 days of freezing temperatures in the region from November till March. The lowest absolute temperature recorded was - 17.4 °C in December. Also, the mean of daily minimum temperature for December, January, February and March was below zero and the mean of daily maximum temperature for December, January and February was -10 °C, indicating the occurrence of cold stress in the region. The results of one-way ANOVA analysis for the investigated genera and species showed that there were significant differences among their traits at 1 % probability level, particularly prior to cold stress. Lolium and Bromus were the most tolerant species among the narrow-leaved forages and the tested germplasm. Among forage legumes, sweet clover exhibited the highest tolerance to cold temperatures. Although the species vicia, Lathyrus and Iranian clover were not tolerant to cold, they were found to be beneficial in terms of soil conservation and sustainability due to the production of proper vegetative cover prior to the cold spell, which lasted till the spring of the next year. Based on the results of this investigation, the studied species and genera can be classified into the following groups:

1- Cold-tolerant forage grasses including accessions of Lolium: 14TN00072, 14TN00038, 14TN00052, 14TN00054 and accessions of Bromus: 10TN00049, 10TN00012, 10TN00036, 10TN00039, and 10TN00026.
2- Cold-susceptible forage grasses such as accessions: KC126013 (L. temelentum) and barley. Although this group was sensitive to cold, they produced good vegetative cover on ground before the occurrence of cold, which can be used as mulch for soil protection throughout the year.
3- Cold-tolerant legumes, such as accessions of Melilotus: 58TN00025, 58TN00047, MahNo313, 58TN00182, 58TN00223, 58TN00140, 58TN00181, 58TN00080, and 58TN00190
4- Cold-susceptible forage legumes: they were categorized into two groups, one group produced good vegetative cover on ground before the cold spell such as accessions 44TN00047, 44TN00041, and 44TN00005, and the other group failed to produce enough vegetative cover on ground such as some accessions of annual medics, Onobrychis, and Trifolium.