Cucurbit Genetics Cooperative Report 15:82-83 (article 32) 1992
Bill Rhodes, Jian Nong Zhang and Xingping Zhang, W.C. Bridges, Jr.
Department of Horticulture, E-142 Poole Agricultural Center, Clemson University, Clemson, SC 29634, USA, Department of Experimental Statistics, F-148 Poole Agricultural Center, Clemson University, Clemson, SC 29634-0367
Rhodes and Love (1) noted that germination rates were severely delayed in some of the crosses among the four genotypes PI 189225 (C), PI 29937 (B) and Citrullus colocynthis R309 (D), and ‘New Hampshire Midget’ (A). Most families from these crosses were observed again in 1991 for germination rates, resistance to anthracnose and resistance to Fusarium wilt. This report deals only with germination rates of the three Citrullus lanatus genotypes and crosses among these three parents.
After the 1983 study, seed were stored in airtight ammo boxes with silica gel at room temperature until the 1991 study. Germination was scored every day for 33 days. Eight-day germination was considered “normal” and later germination was considered “delayed”,. Germinating at 8 days from the 1991 study were compared with germination data from the 1983 study. Delayed and total germination were also recorded in 1991. In the 1983 study, 288 seed of the parents and 96 seed of the progeny were planted. In the 1991 study, 50 seed of each family were planted in most cases.
Results of these comparisons are given in Table 1. Germination rates are grouped into families from one or more original crosses.
The germination of New Hampshire Midget in 1991 was much lower than it was in 1983. However, 8-day germination of PI 299379 (B) and PI 189225 (C) was significantly higher 8 years after the original study, and 33-day germination was 83% and 94% for the two PI’s, respectively.
Generally, loss of 8-day germination over the 8 year period occurred in the presence of the NHM genome: AxB, A(AxB), A(AxC), and (AxC)A. Gain of 8-day germination over the 8 year period occurred in backcrosses to B: B(AxB), (BxC)B. Gain of 8-year period occurred in AxC, CxB, and (BxC)C. After 8 years, 8-day germination percentages increased in parents B and C and in 14 out of 17 populations from these parents.
The results from some of the AxB crosses suggest maternal recessive control of delayed germination in B. The F1 population germinates at 8 days like parent A. Eight-day germination in the F2 in ’83 is less than parent A or the F1, suggesting that the population is segregating for delayed germination. When B was the maternal parent in the backcross B(AxB), germination in was delayed in 1983 and 1991.
The results from the AxC crosses are even more complex. The C genome delays germination only in the F1 and in the backcross C (AxC) in 1983. In 1991, early and total germination are increased in the F1 , but decreased in the backcross A(AxC). However, the reciprocal backcross (AxC)A germinates slowly but completely after 8 years.
These results suggest that different factors retard rapid germination in fresh seed and prolong viability in old seed of PI299379 and PI 189225, and that these factors deteriorate with time, The deterioration of these germination inhibitors makes it impossible to distinguish them simply by scoring germination after 8 years in families from crosses of the two PI’s. The use of fresh seed from new crosses of inbred lines, complete germination data over a 30-day period and biochemical analysis might lead to an understanding of the inheritance of these factors. These factors may benefit the species by maintaining seed viability over a longer period.
Table 1. Percent germination and rates of seed from Citrullus lanatus ‘New Hampshire Midget’ (A), PI 299379 (B) and PI 289225 (C) and F1, F2 and BC progeny in 1983 and 1991.
Parent or Progeny |
’83 8-day |
’91 8-day |
’91 delayed |
’91 Total |
| Parents: A | 64a | *16 a | 14 b | 30 c |
| B | 1 b | * 31 b | 52 a | 83 a |
| C | 1 b | * 90 c | 4 b | 94 a |
| F1 (A x B) | 68 | 28 | 28 | 56 |
| F1(B x A) | 65 | – | – | – |
| F2(A x B) | 51 | * 82 | 6 | 88 |
| A (A x B) | 40 | * 22 | 8 | 30 |
| (A x B) A | 44 | ns 56 | 24 | 80 |
| B (A x C) | 14 | * 34 | 54 | 88 |
| (A x C) C | 38 | * 84 | 4 | 88 |
| F1(A x C) | 7 | * 73 | 24 | 97 |
| F2 | 83 | * 1 | 82 | 83 |
| A (A x C) | 80 | * 6 (1) | 10 | 16 |
| 23 (2) | 37 | 60 | ||
| (A x C) A | 89 | * 34 | 64 | 98 |
| C (A x C) | 53 | – | – | – |
| (A x C) C | – | 54 | 30 | 84 |
| F1 (B x C) | 7 | ns 4 (1) | 4 | 8 |
| 46 (2) | 0 | 46 | ||
| F1(C x B) | 1 | * 55 | 45 | 90 |
| F2 (B x C) | 0 | * 6 (1) | 44 | 50 |
| 12 (2) | 14 | 26 | ||
| (B x C) B | 0 | * 54 | 8 | 62 |
| C (B x C) | 50 | 33 (1) | 42 | 75 |
| 82 (2) | 4 | 86 | ||
| (B x C) C | 12 | * 50 | 18 | 68 |
Small letters denote differences between parents. * denotes differences between 8-day germination in ’83 versus ’91. The LSD statistic with an alpha of 0.05 was used.
Literature Cited
- Rhodes, B.B. and Stephen L. Love. 1983. Presence of factors for delayed germination in Citrullus lanatus and Citrullus colocynthis CGC 6:64-65.