Differential lines and controls: seed handling and seedling raising

A separate and rust-free area must be maintained to keep seed materials used for race identification clean and free of contaminants. Seeds of each differential and susceptible check must be stored in clearly labeled, separate glass or plastic containers with lids, and kept in a cool area — cold room or refrigerator, if available (Fig. 2).

For raising seedlings, use sterilized soil composed of three different materials: soil, sand, and farm yard manure mixed at the ratio of 2:1:1 by volume. Seedlings are raised by two methods.

  • One method is to pre-germinate seeds by spreading the seeds on filter paper in petri dishes, moisten with water and close the lid. On the third day, the seeds will germinate and the radicles are seen. Then these germinating seeds are planted in pots using forceps (Fig. 3).
  • A second method is direct planting of the seeds in pots filled with sterilized soil. More uniform seedling germination is normally achieved by using the first method (Fig. 4). In both methods, at 7-8 days after planting, the primary/first leaf will be fully extended and the second leaf will be 2-4 cm long. This is the right stage for inoculation with rust pathogen spores in the greenhouse.

Seeds of a highly susceptible host (for example, McNair) are planted to multiply the rust collected from the field sample to be analyzed. Once the sample is increased sufficiently, the 20 current standard stem-rust differential lines (Table 1) are planted for race designation. It is critical that the seedling raising-room be free from rust spores. Rust-free protective gowns must be worn when activities are going on in the room. Different sized clay and plastic pots are used according to the needs of the activity to be conducted. Trays are used to group the pots in order (Fig. 5).

Table 1: Wheat Stem Rust Differential Lines (accessions deposited at the National Plant Germplasm-Aberdeen, ID)


Number

Sr gene

Line name

Habit

501

Sr5

ISr5-Ra

Spring

502

Sr21

CnS_T_mono-derivative

Spring

503

Sr9e

Vernstein

Spring

504

Sr7b

ISr7b-Ra

Spring

505

Sr11

ISr11-Ra

Spring

506

Sr6

ISr6-Ra

Spring

507

Sr8a

ISr8a-Ra

Spring

508

Sr9g

Acme

Spring

509

Sr36

W2691SrTt-1

Spring

510

Sr9b

W2691Sr9b

Spring

511

Sr30

BtSr30Wst

Spring

512

Sr17 (+Sr13)

Combination VII

Spring

513

Sr9a

ISr9a-Ra

Spring

514

Sr9d

ISr9d-Ra

Spring

515

Sr10

W2691Sr10

Spring

516

SrTmp

CnsSrTmp

Spring

517

Sr24

LcSr24Ag

Spring

518

Sr31

Sr31/6*LMPG

Spring

519

Sr38

VPM1

Winter

520

SrMcN

McNair 701

Winter