Fruit maturity and seed moisture content affect seed storage in papaya (Carica papaya L.)

Wen-Ju Yang1, Yu-Ju Ho1, I-Cheng Chen2 and Ting-Lin Chang2

1Department of Horticulture and Landscape Architecture, National Taiwan University 2Taiwan Seed Improvement and Propagation Station, COA

Papaya (Carica papaya L.) seed, one of the important seed for exportation in Taiwan. The storage of papaya seeds, a kind of intermediate seeds, are sensitive to storage temperature and affected by seed moisture content and fruit maturity at harvest. The research data for building up a standard protocol for seed production is not sufficient up to date. Therefore, we are aimed to evaluate how fruit maturity and moisture content affect seed storage.

The moisture content of fresh seeds ranged between 60.2% - 65.3%. Seed moisture content was balanced to expected level at 15oC under low humidity. For maturity test, the fruits of -3 to +1 weeks relevant to the stage at 22 weeks after pollination (WAP) were harvest. Half of the immature fruits were ripening for 3 and 6 days before seed harvesting. Seed will be balanced to approximately 10%. For moisture content test, the seed moisture content was 30.6% - 8.3%. The seeds were stored at 0, 5, 10oC to evaluate storage span and germination test was according to the ISTA rule for papaya. The first and final germination was counted at 12th and 28th day, designed as Gfgp and G1stgp.

Fig. 2. The effect of fruit maturity on seed germination in ‘Sun Lady’. Fresh (F) and 10% moisture content (C) seeds were tested. (Bar=10 cm)

The seed germination of the fruits harvested at the groove-ripen stage was near 100. Immaturity may decrease seeds germination, and lowing the moisture content to the level of commercial seeds (10%) increased their germination (Fig. 2).

Seeds with higher moisture content were more sensitive to lower temperature and intolerant to storage (Fig. 1). Seeds with 30.6% moisture content showed rapid decrease after 3 months of storage at all 3 temperatures. Seeds of 8.3% showed its tolerance to 0oC storage by high Gfgp and G1stgp (vigor). Gfgp showed that seeds of 12.3% - 9.8% were tolerant to 5oC and seeds of 21.7% - 16.4% were safe for storage at 10oC; however, the relevant G1stgp revealed that the vigor was affected by higher moisture content.

Materials and Methods The Effect of Fruit Maturity on Seed Storage

The Effect of Moisture Content on Seed Storage

23 WAP

22 WAP

21 WAP

20 WAP

19 WAP

Weeks after pollination (WAP)19 20 21 22 23

Germ

inat

ion

(%)

0

70

80

90

100

FC

F C

20 WAP+3 RD

0 3 6 9 12 15 18 21 240

20406080

100

20 WAP+6 RD

Storage period (month)

0 3 6 9 12 15 18 21 24

19 WAP+3 RD

0 3 6 9 12 15 18 21 24

19 WAP+6 RD

0 3 6 9 12 15 18 21 24

23 WAP

Ger

min

atio

n (%

)

020406080

100

0¢J5¢J10¢JFresh

Gfgp

22 WAP 21 WAP 20 WAP 19 WAP

20 WAP+3 RD

0 3 6 9 12 15 18 21 240

20406080

100 20 WAP+6 RD

Storage period (month)

0 3 6 9 12 15 18 21 24

19 WAP+3 RD

0 3 6 9 12 15 18 21 24

19 WAP+6 RD

0 3 6 9 12 15 18 21 24

23 WAP

Ger

min

atio

n (%

)

020406080

100

G1stgp

22 WAP 21 WAP 20 WAP

19 WAP

Fig. 3. The effect of fruit maturity on seed storage in ‘Sun Lady’. Gfgp and G1stgp represented final germination and first germination percentage. RD represented ripening days.

16.4%

0 3 6 9 12 15 18 21 240

20

40

60

80

100

12.3%

Storage period (month)

0 3 6 9 12 15 18 21 24

9.8%

0 3 6 9 12 15 18 21 24

8.3% (commercial)

0 3 6 9 12 15 18 21 24

30.6%

Germ

inat

ion

(%)

0

20

40

60

80

1000¢J5¢J10¢JFresh

21.7% 18.3% 17.0%

Gfgp

16.4%

0 3 6 9 12 15 18 21 240

20

40

60

80

100

G1stgp

12.3%

Storage period (month)

0 3 6 9 12 15 18 21 24

9.8%

0 3 6 9 12 15 18 21 24

8.3% (commercial)

0 3 6 9 12 15 18 21 24

30.6%

Germ

inat

ion

(%)

0

20

40

60

80

1000¢J5¢J10¢JFresh

21.7%

18.3%

17.0%

Fig. 1. The effect of moisture content on seed storage in ‘TN1’. Gfgp and G1stgp represented final germination and first germination percentage.

Conclusion Seeds from mature fruits and mediated the seeds moisture content to be ~8.3% is suggested. If the fruit color is not yet completed yellowed, 3 days of ripening is recommended; however, the fruit maturity should be at least mature green. 10oC is a safer storage temperature, in terms of higher vigor.

Seeds harvested from fruits closed to full yellowed could maintain their germination at all 3 storage temperature over the 24 months experimental period, and seeds from not fully mature fruits showed sensitivity to lower temperature storage (5 and 0oC) (Fig.3). Three days of ripening of the mature green fruits (20 WAP) may resume their ability of storage at 5 and 0oC but not immature green fruits (19 WAP). The vigor was also affected by immaturity.