Cucurbit Genetics Cooperative Report 6:24 (article 12) 1983
A.P.M. den Nijs and I. W. Boukema
Institute for Horticultural Plant Breeding, P. O. Box 16, Wageningen, The Netherlands
In a previous program to introduce parthenocarpy into the pickling cucumber, de Ponti (unpublished data) noticed distinct differences between breeding lines in their sensitivity to low relative humidity (RH). Newly-formed leaves of sensitive plants expanded unevenly: the leaf margin grew less than the leaf blade, resulting in downward (or sometimes upward) curled leaves reminiscent of an umbrella. Similar symptoms are caused by toxic concentrations of boron in the soil or nutrient solution. Occasionally, the phenomenon occurs in standard cultivars when a period of cloudy weather is followed by strong, dry winds under open sky, causing a fast decline in the relative humidity of the glasshouse.
The character appeared to be recessively inherited. Appropriate crosses were made, and analyzed using the Chi-square test, Samples of two F2 populations, along with the reciprocal F1s and the sensitive and nonsensitive parent, were grown on glasshouse benches in the summer of 1981 and 1982. The plants were kept under a tent of clear plastic for 14 days following transplanting in order to keep the RH high. Temperature was approximately 26°C day/20°C night, The symptoms showed approximately one week after the removal of the tent (drop in RH). Virtually all plants could clearly be classified as either normal or sensitive. The results of the tests were remarkably similar (Table 1).
We concluded from the data that the sensitivity is controlled by one single recessive gene. In view of the characteristic shape of sensitive leaves and according to the rules for nomenclature of cucurbit genes, we propose to designate the gene umbrella leaf (ul). The exact origin of the mutant in our material could not be traced, We emphasize that the expression of the gene depends somewhat on the environment. This makes the gene an interesting character for plant physiological studies into the nature of leaf development. The gene is being used in linkage studies at our institute.
Table 1. Frequencies of sensitive (ul) and normal plants in progenies from crosses involving umbrella leaf.
Generation |
1981 Normal> |
1981 Sensitive |
1982 Normal |
1982 Sensitive |
Ratio of
|
X2 for 3:1 |
| P1 sensitive | 1 | 10 | 0 | 10 | 1:20 | – |
| P2 normal | 8 | 0 | 10 | 0 | 18:0 | – |
| F1 (P1 x P2) | 24 | 0 | 18 | 0 | 42:0 | – |
| F1 (P2 x P1) | 23 | 0 | 20 | 0 | 43:0 | – |
| F2 (P1 x P2) | 79 | 23 | 75 | 23 | 3.3:1 | 0.43ns |
| F2 (P2 x P1) | 83 | 23 | 81 | 19 | 3.9:1 | 2.33ns |