Characterization of freezing tolerance and vernalization in Vern-, a spring-type Brassica napus line derived from a winter cross

Abstract

Exposure of winter brassicas to periods of low temperature decreases the transition required from vegetative to reproductive growth. This low-temperature exposure also results in the acquisition of freezing tolerance. To investigate the relationship between vernalization and freezing tolerance, homozygous microspore-derived (DH) lines were developed from reciprocal crosses between two winter cultivars of Brassica napus L., cv. Cascade and cv. Rebel. A resulting line, termed Vern-, expressed a high degree of freezing tolerance and was selected for study. Analysis of growth and development revealed that Vern- is a true spring type, having completely lost the vernalization requirement. Using markers previously mapped in B. rapa, it was concluded that Vern- inherited freezing-tolerance alleles from Cascade. With regard to vernalization and flowering time, Rebel, although traditionally classified as a winter type, carries spring alleles at the major and some of the minor loci. Vern- inherited these alleles from Rebel, in addition to one spring allele from Cascade. Thus, spring alleles from both parents were critical in establishing the spring phenotype observed in Vern-.

Temperatura basal, duração do ciclo e constante térmica para a cultura do crambe

“…Enquanto plantas jovens de crambe são severamente danificadas a -1 ºC, de forma geral, plântulas de canola, em estádio cotiledonar, morrem sob temperatura de -3 ºC e -4 ºC. Sob não aclimatação, plantas de canola morrem rapidamente a -4,6 ºC, enquanto plantas com cinco ou mais folhas, crescendo em ambiente com temperatura média do ar inferior a 18 ºC resistem a geadas de até -8,6 ºC (Rapacz, 1999;Hawkins et al, 2002).…”

Aclimatação ao frio e dano por geada em canola

“…geada (Hawkins et al, 2002;Smallwood & Bowles, 2002;Gusta et al, 2004;Asghari et al, 2008;Stavang et al, 2008). …”

“…Gusta et al (2004) observaram que, em plantas não aclimatadas e sob condições de baixas temperaturas, a morte de folhas é rápida a -4,6ºC. Porém, plantas com cinco ou mais folhas, quando crescem em ambiente com temperatura média do ar inferior a 18ºC, podem resistir a geadas de -8,6ºC (Rapacz, 1999;Hawkins et al, 2002) e -12ºC, no caso de canola de inverno (Rife & Zeinali, 2003).…”

“…A aclimatação induz mudanças morfológicas, fisiológicas, bioquímicas e moleculares que tornam as plantas resistentes não somente a temperaturas congelantes, mas especialmente à desidratação provocada pelo congelamento (Rapacz, 1999;Hawkins et al, 2002;Gusta et al, 2004;Tasseva et al, 2004;Asghari et al, 2008;Stavang et al, 2008).…”

Haploids in the Improvement of Crucifers

“…Furthermore, Hawkins et al (2002) have shown by using DH populations derived from crosses between the B. napus cultivars 'Cascade' and 'Rebel', with different freezing tolerance and vernalization requirements (Cascade has an obligate vernalization requirement and is highly freezing tolerant, while Rebel has a weak vernalization requirement and little freezing tolerance) that both traits can be separated and the positive trait expressions combined. The authors suggest that one of the developed DH lines is of particular importance because it lacks a vernalization requirement (Vern-) and possesses a high degree of freezing tolerance.…”