Genotypic Variations in Seed Dormancy in a Segregating Population of Barley

Abstract

Pre-harvest sprouting (PHS) in barley (Hordeum vulgare L.) can cause economic losses especially in malting barley. Seed dormancy is where viable kernels fail to germinate under optimum conditions of moisture, oxygen, and temperature. The objective of this study was to determine the level and range of seed dormancy in a population of 239 F₆-derived F₇ lines of barley from a cross with ‘Samson’ (a variety with high seed dormancy) background. These lines were grown in the field at the Field Crop Development Centre, Lacombe, Alberta. The spikes were harvested when the kernels were at approximately 25% moisture content on a wet weight basis and dried to 12% moisture content with minimal after-ripening and stored at -15^oC before hand-threshing and germination. For each genotype, 25 seeds were placed in Petri dishes for germination in two replicates under controlled dark environment at 18^oC. Daily counts of germinated seeds were made and dormancy levels were calculated using a weighted germination index (WGI). Genotypic effects on WGI were highly significant (P</=0.01). The WGI ranged from a low (high dormancy) of 0.02 to a high (no dormancy) of 1.00. A wide range of seed dormancy levels can be found within barley genotypes and this suggests multiple genes or factors are controlling dormancy levels in this barley population. The results show a wide range of seed dormancy levels among lines in the barley population of the current study.

Background

Preharvest sprouting can cause serious economic losses in malting barley exposed to moist conditions prior to harvest. This sprouting although not visible results in dead kernels in the malting process. In non-malting varieties such as ‘Samson’, dormancy has been identified. Several factors can contribute to increased resistance to PHS: decreased levels of alpha-amylase activity in the grain, the presence of germination inhibitors, decreased water absorption by the grains and altered responses to hormones, among others (2,3). Improving overall dormancy in non-malting barley should be of benefit to the seed industry, producers and end-users. The main effects of PHS are a lower yield due to harvest losses and more importantly, a reduction in end-product qualities. Barley products obtained from sprouted grain could make poor malt, feed and food due to starch breakdown resulting from high alpha-amylase activity (3).

Objectives

The objectives of this study were:

• To determine the genotypic variations in seed dormancy of a barley population comprising 239 lines (genotypes).
• To determine the levels of seed dormancy and seed sensitivity to germination in the current population of barley.

• A population of 239 barley lines was grown in the growth room in 30 cm-rows at the Field Crop Development Centre near Lacombe, AB.
• Intact spikes of each line with kernels at about 25% moisture content (wet basis) were hand-harvested.
• Spikes were dried down to about 12% kernel moisture content and stored in a –15^oC freezer to avoid after-ripening maturation.
• The spikes were hand-threshed to minimize mechanical damage of kernels, and these were used for germination.
• For each line, 25 kernels per Petri plate and replicated 2x were incubated in a germination chamber at 18^oC and >95% relative humidity for 6 days.
• Each plate was checked daily for germination. Seeds were considered germinated when the radical was 1 mm long.
• Germinated seeds were counted and removed from the Petri dishes.
• A weighted germination index (WGI) as described by Reddy et al. (1985) was calculated
  WGI = {6 x n1 + 5 x n2 +……..+ x n6} / 6 x N
  Where n1, n2, ….., n11 = seeds germinated on 1st, 2nd until 6th day. N is total number of seeds placed for germination.
• Data was analyzed using SAS statistical program.

• The analysis of variance showed genotypes were significantly (P</=0.01) different in seed dormancy, and contributed to 97.6% of the observed variation, and the remainder of the variations (2.4%) attributed to replicates and random error.
• Genotypes with low seed dormancy germinated quickly, whereas those with high seed dormancy germinated slowly or failed to germinate any seed, within 6 days.

• Genotypes showed a wide range of seed dormancy with WGI mean values varying from 0.01 (dormant) to 1.00 (susceptible) (Fig. 1).
• Out of 239 lines, 58 showed WGI mean values of between 0.02 and 0.50; and 179 lines were between 0.51 and 1.00 (Fig. 1).
• Genotypes with relatively high levels of seed dormancy (i.e, with low WGIs) (Fig. 2), and genotypes with relatively low levels of seed dormancy (i.e with high WGIs) (Fig. 3) were identified.

• This study of 239 lines showed a wide range of genotypic variations in seed dormancy.
• The wide range of seed dormancy suggests there could be multi-genes controlling the expression of seed dormancy in this population.
• Our method showed the possibility of screening a large population of barley lines for different levels of seed dormancy in a short period (6 d).
• A short screening period is important for barley cultivar development programs. Plate 1 shows germination differences of 4 genotypes on day 2.
• Genotypes with hulless seed types showed relatively low levels of seed dormancy compared with genotypes with hulled seeds. This indicates that the hull could be inhibiting germination.