Near-Isogenic Lines of Several Cucumber Varieties

admin

Cucurbit Genetics Cooperative Report 8:4-6 (Article 2) 1985

Henry M. Munger
Cornell University, 410 Bradfield Hall, Ithaca, NY 14853

In over 40 years of cucumber breeding at Cornell, a number of near-isogenic lines have been bred by the backcross method. A few have been released as varieties and the rest as germplasm, but not all of the latter have had formal release notices because of their minor importance. A complete listing to date is given in Tables 1 and 2, and seed in small amounts is available from the author. These are being deposited in the National Seed Storage Laboratory as sufficient seed is produced.

The background genotypes are all well-known as commercial varieties except for the Cornell 551 series. 55-551 is a white spine pickle based largely on Stays Green but not derived from a true backcross program. Its chief value is in having a level of cucumbermosaic (CMV) resistance comparable to Tablegreen, considerably higher than any other pickle we have tested.

Most of the genes incorporated by backcrossing are well known except for mildew resistance and dwarfness. Mildew resistance in all our material other than Poinsett is from Spartan Salad and appears to be conditioned by two recessive genes which have not been identified with those given gene symbols. Dwarfness is derived from Hardin’s PG57 and is initially selected as a single recessive gene which shortens the hypocotyl of seedlings. Within this group there has been selection for a wide range of mature plant types, from extreme dwarfness in Spacemaster and 78-515, a dwarf version of SR551, to only slight vine size reduction in the Marketmore and SMR18 dwarfs. All have been selected for greater earliness than the recurrent parents. Consequently the dwarf lines are not truly near-isogenic but are listed as a convenient way of letting people know of their existence and availability.

Except for the dwarfs, most lines have been backcrossed 5 times to the recurrent parent but in some cases several more backcrosses were made. The most extreme dwarfs have only 3 backcrosses to Tablegreen and SR551, respectively, but the Marketmore dwarf has a total of 7 with the last 5 to Marketmore 76. The SMR18 dwarfs have had 3 and 5 backcrosses, respectively, to some version of SMR18.

Table 1. Characteristics of Cornell Cucumber Variety and Germplasm Releases of Slicing Type.

table 1

1V = Variety, G = Germplasm, T = Trial.
2Powdery mildew resistance (PMR) and downy mildew resistance (DMR) are closely associated and in most cases, the level of one is indicative of the level of the other. Apparent PMR varies with conditions; it is lower when temperatures and light intensity are low, when plants are becoming senescent, and when there is abundant inoculum from susceptible plants nearby.
3Resistance to target leafspot caused by Corynespora cassiicola. x = resistant, – = susceptible in greenhouse tests at Ithaca. Same symbols in ( ) = presumed reaction based on isogenicity but not actually tested.

Table 2. Characteristics of Cornell Cucumber Variety and Germplasm Releases of Pickling Type.

Resistance to

1985
Status1

Unif.
color
u

Non-
bitter
bi

Gynoec.
F

Dwarf

CMV

Scab
Ccu

PM+DM2

Bact. wilt
Bw

TLS3
Cca
 

Near-Isogenic Lines with Cornell 551 Background Genotype

 

55-551

G

–

–

–

–

High

–

–

(x)

SR551

G

–

–

–

–

High

x

–

–

x

SR551F

G

–

–

x

–

High

x

–

–

(x)

SR551 u

G

x

–

–

–

High

x

–

–

(x)

SR551 uF

G

x

–

x

–

High

x

–

–

(x)

PMR 551

G

x

–

–

–

High

x

Med.-High

–

–

PMR 551F

G

x

–

x

–

High

x

Med.-High

–

(-)

SR551 Bw

G

x

–

–

–

High

x

–

x

(x)

PMR551 Bw

G

x

–

–

–

High

x

Med.-High

x

(-)

78-515

G,T

–

–

–

x

High

x

–

–

(x)

Near-Isogenic Lines with Wisconsin SMR18 Background

SMR18 WS

G

–

–

–

–

Med.

x

–

–

x

SMR18 WSF

G

–

–

x

–

Med.

x

–

–

(x)

SMR18 u BS

G

x

–

–

–

Med.

x

–

–

(x)

SMR18 u BSF

G

x

–

x

–

Med.

x

–

–

(x)

SMR18 u WS

G

x

–

–

–

Med.

x

–

–

(x)

SMR18 u WSF

G

x

–

x

–

Med.

x

–

–

(x)

PSMR18 WS

G

–

–

–

–

Med.

x

Med.-High

–

–

PSMR18 WSF

G

–

–

x

–

Med.

x

Med.-High

–

(-)

Dwarf SMR18 u

T

x

–

–

x

Med.

x

–

–

(x)

Dwarf PSMR18 WS

T

–

–

–

x

Med.

x

Med.-High

–

(-)

1V = Variety, G = Germplasm, T = Trial.
2Powdery mildew resistance (PMR) and downy mildew resistance (DMR) are closely associated and in most cases, the level of one is indicative of the level of the other. Apparent PMR varies with conditions; it is lower when temperatures and light intensity are low, when plants are becoming senescent, and when there is abundant inoculum from susceptible plants nearby.
3Resistance to target leafspot caused by Corynespora cassiicola. x = resistant, – = susceptible in greenhouse tests at Ithaca. Same symbols in ( ) = presumed reaction based on isogenicity but not actually tested.