Cucurbit Genetics Cooperative Report 18:17-18 (article 8) 1995

Effect of Hot Treatment on the Vigor of Newly-Harvested Cucumber Seeds

Hongwen Cui and Mingan Yin

Dept. of Horticulture, Northwestern Agricultural University, Yangling, Shannxi 712100, P.R. China

Newly-harvested cucumber (Cucumis sativus L.) seeds pass through a physiological process called "after-ripening" before they are sown in China (2). Newly-harvested seed have low vigor and seedling establishment is often difficult. Xie (1) soaked newly-harvested cucumber seeds in H₂O₂ to increase seed vigor and observed a positive seedling growth response. This experiment describes the effect of extreme temperature treatment on the vigor of newly-harvested cucumber seeds.

Methods. Seeds of 'Jinyan 6' were taken from mature fruits and fermented on July 16. Seeds were washed and dried in the sun on July 18, and the experiment was initiated in the evening of the same day.

The experiment had two temperature treatments [hot (75C) and cold (-4C)] and two seed treatments (newly-harvested seeds and seeds stored for one year). Three replications were made in time. The experimental design proceeded stepwise as follows: 1) treating, 2) soaking, 3) germinating. Newly-harvested seeds were treated at either high temperature or low temperature for 24 hours, soaked in water together with control seeds (ck 1) for 6 hours, and then germinated at 30C. From the time when stored seeds (ck 2) just sprouted, germination number was recorded every 6 h for 3.5 days. Germination percentage, GS, PV, GI and MLIT were calculated. GS calculation was made at 1.75 days. When a seed's radicle length was half that of the seed's length, seeds were sown in a flower-pot (soil), and grown for observation in the seedling stage.

Results. Data show (Table 1) that there was no significant difference between new-harvested seeds and stored seeds in germination percentage representing viability, but there were significant differences in other indices representing vigor. This indicates that newly-harvested seeds have low vigor during the after ripening phase.

Hot treatment increased GS, PV and GI, and shortened MLIT greatly, indicating that hot treatment increased the vigor of newly-harvested cucumber seeds. Differences in seed vigor were also detected between not-treated seeds and controls (ck2). Cold treatment had no effect on increasing the vigor of newly-harvested cucumber seeds. Data indicate that improved seedling growth was consistent with high germination rate, and that hot treatment had an effect on promoting good plant growth (Table 2).

Discussion. Xie (1) concluded that the effect of H₂O₂ solution was due to its O₂ release which met the needs of germination. Theoretically, H₂O₂ decomposes into H₂O and O₂, and is metabolized by the seeds. It is believed that these events promote aerobic respiration in the seed and changed its oxidation-reduction pathways. Such alterations produce a metabolism which is favorable to germination. The seed-peeling treatment in Xie's experiment showed no favorable effect. So it can be concluded that the dormancy in newly-harvested cucumber seeds is not caused by limitations imposed by the seedcoat. The effect of hot treatment in our experiment can not be explained by changes in seed coat structure. Fu (2) found that hot treatment could shorten the after- ripening period in cluster mallow (Malva verticillata L.) seeds and could increase germination rate. We believe that hot treatment can accelerate a cucumber seed's after-ripening period.

Table 1. Germination characteristics of cucumber (Cucumis sativus L.) seeds treated with hot and cold temperatures.

 

Treatment	GP (%)	GS (%)	PV	GI	MLIT
Hot treatment	96 az	70 B	35.2 ABb	28.2 B	0.89 Bb
Cold treatment	96 a	40 Cc	22.8 Bbc	24.2 Cc	1.04 ABa
CK1 (new)y	95 a	34 Cc	18.1 Bc	23.2 Cc	1.08 Aa
CK2 (stored)x	99 a	98 A	50.5 Aa	36.3 A	0.69 Cc

^z Numbers in table was tested by LSR. Capital letters indicate tests at a=0.01, and small letters a=.05.
^y Control treatment of newly-harvested seed.
^x Control treatment of seed stored for one year.

Table 2. Vigor of cucumber (Cucumis sativus L.) seedlings from seeds treated with various temperatures before sowing.

Treatment	July 22	July 24	July 25	July 26
Hot treatment	sown	3.0 cm high	9.1 cm high, cotyledons parted	11.0 cm high, main root 2.8 cm long & thick
Cold treatment	sown	outcropped	5.7 cm high, cotyledons unseparated	8.0 cm high, cotyledons unseparated, main root 1.7 cm long, thin
CK1 (new)z	sown	outcropped	4.4 cm high, cotyledons close together	6.0 cm high, cotyledons unseparated, main root 1.5 cm long, thin

^z Control treatment of newly harvested seed.

Literature Cited

1. Xie, Wenhua. 1985. Cucumber seeds' rest and effect of H₂O₂ on their germination. Chinese Vegetables 2:1.
   
2. Fu, Jarei. 1985. Seed Physiology. Science Press:183.