Seed
Pest and disease levels and the physiological age of seed are important in growing successful crops.
In the Mid West, growers are both purchasers and growers of seed. Seed supplied from the South West is too physiologically young for autumn sowings so growers bulk seed in a winter sowing for one generation so it is the right age for planting the following autumn.
The procedure is to plant seed that has been multiplied through four field generations (G4) and harvest the fifth field generation (G5) in spring so it is the right age for planting the following autumn.
For these seed crops it is important to use G4 seed of the highest quality, such as certified seed from the WA scheme, and to manage crops so the resulting G5 is of high quality. High quality source seed and vigilant seed crop management are vital.
Insect monitoring showed aphid numbers to be higher than in traditional summer growing seed areas in the South West. Virus monitoring showed aphid-borne potato leafroll virus (PLRV) was often present where aphid control was excellent. Other viruses such as potato virus S (PVS) were also found in crops grown from seed that was assumed to have very low level of viruses.
Selection
For seed, ware or crisp crops, use high quality seed of the correct variety. For a seed crop bulked once or twice, select higher quality ‘certified’ seed than for a non-seed crop. Choose varieties to suit growing conditions and market requirements.
Growing a non-approved variety could lead to buyer rejection and significant loss of income. Once the right variety is selected, use high quality seed.
Sanitary quality
Seed schemes focus on sanitary quality so that buyers of certified or registered seed can be assured that it meets minimum standards of disease and pest incidence and is of high quality. To minimise the risk of viruses and other infections, use certified or registered seed from Western Australian Seed Potato Producers Inc. (WASPP).
WASPP seed is subject to either the ‘Western Australian Certified Seed Production Rules’ or ‘Western Australian Registered Seed Production Rules’. Application of the rules is overseen by DAFWA inspectors who examine crops twice during growth and tubers once after harvest. Growers can be trained to become Accredited Tuber Inspectors (ATI) which qualifies them to conduct their own inspections.
The number of generations (G) over which seed crops can be multiplied is limited. The maximum is five (G5) for certified seed. Each generation of seed crop must comply with strict rating standards based on field inspections for disease, foreign varieties and permitted disease/nematode infection levels in tubers.
A list of seed growers is published annually in the ‘WA Grower’. This provides information on where a seed crop is grown, generation, variety and expected harvest date. The rating of seed crops can be discussed with seed suppliers.
Updated information may also be obtained from the Senior Seed Certification Officer at the Manjimup Horticultural Research Institute on +61 (0)8 9777 0000.
Physiological age
In the Mid West, the main crop is autumn-planted for which seed of an appropriate physiological age is not readily available. In WA, most seed potatoes are produced in the South West and harvested in summer/autumn to suit sowing from winter to spring. This seed is unsuitable for early autumn sowing. Growers must either obtain seed from producers who can supply seed at the correct age or produce their own.
Own-seed growers will need to grow their crops for at least one generation, usually from G4 to G5, sowing in winter, harvesting in spring and storing over summer. This seed will be an appropriate physiological age for rapid emergence the following autumn.
If you plan to sell a portion of a commercial crop for seed (for example, small fraction of Atlantic crisp crop for seed export) you must buy in G3 seed which, after the autumn multiplication, will produce G4 seed which can be used to produce G5 (oldest generation permitted for certified seed) from your commercial crop.
Although physiological age is important, it is not assessed by seed schemes. It is related to dormancy and therefore planting time, emergence and market requirements for tuber size and number. It can be inferred from harvest date, postharvest storage conditions and, after sprouting, from sprout number, length and the position on the tuber.
There is also opportunity to assess germination percentage and adjust seeding to account for low rates. Low germination percentage may indicate seed that is too young (dormant) or too old (senile).
Selecting quality seed
It is important that G3 or G4 seed purchased for bulking in the Mid West be of high quality because of greater aphid infestation and possible virus transmittance compared with traditional seed areas. Within the WA seed potato schemes, growers can choose seed with different disease ratings determined during field inspection.
At each inspection, the crop is given a rating of 1 to 3, with rating 1 having the lowest disease incidence and rating 3 having the highest allowable. As Mid West growers will need to grow their own seed for at least one generation, buy seed of rating 1 (see Table 1) to be sure of achieving high quality seed, after one or two bulkings — usually from G3 or G4 to G5 — for subsequent commercial crops.
|
| Rating 1* | Rating 2 | Rating 3 | |||
|---|---|---|---|---|---|---|
| Inspection | 1st | 2nd | 1st | 2nd | 1st | 2nd |
| Factor | % of plants | |||||
| Foreign varieties | 0.05 | 0.00 | 0.1 | 0.01 | 0.10 | 0.10 |
| Viruses | 0.10 | 0.01 | 0.25 | 0.10 | 1.00 | 1.00 |
| Other diseases | 0.25 | 0.10 | 0.5 | 0.25 | 2.00 | 2.00 |
| Total | 0.25 | 0.10 | 0.5 | 0.25 | 2.00 | 2.00 |
* All rating 1 crops must be 0% for potato virus Y at the first and second crop inspections.
Rating 1 seed has the lowest tolerance level for virus infection (10 and 100 times less than rating 2 or 3 seed respectively) and therefore represents the greatest chance that the virus will not be introduced to farms where seed is produced.
Planting
Planting time will vary according to growing conditions and the planned harvest or delivery date, which is set by market requirements.
In sandy soils, planting before early March is risky due to possible poor germination in hot soil. Similarly, harvesting in hot conditions after mid-November may result in excess harvest damage.
Seed type
Whole seed is preferred for sowing in warmer autumn months as cut seed has higher risk of breakdown in hot soil. Cut seed is an option for winter sowings. In- and between-row spacings will be determined by variety and market requirements and it is important to get them as accurate as possible.
Planting at too low or too high a density may lower yield, leading to economic loss. Check the spacing between seeds and rows early in the planting operation and adjust as necessary. Be sure you know the likely germination per cent or dormancy of the seed so you can adjust seed rate for low emergence.
Treatment
Seed is usually treated with fungicide to protect it from diseases such as Rhizoctonia and Fusarium in the early stages.
In warm sandy soils, use dry powder rather than liquid formulations to minimise the risk of seed breakdown that could result from excess water on the tuber surface.