Pathogens
The main seed-borne pathogens of Pisum sativum are listed in Table 11.1.
been selected which are suitable for the fresh crop and processing. The majority of cultivars are bush types but there are also climbing (‘pole’) types which are frequently referred to as ‘climbing French bean’.
Cultivar decription of French bean
● Season and use: flowering and cropping season, suitability for specific market outlets, e.g. green, processing or dried, suitability for mechanical harvesting.
● Seed: relative length, testa colour and patterning, bars or mottle, if bicol- oured, shape resistance to mechanical damage.
● Plant habit: dwarf or climbing, bush types degree of branching.
● Leaf: colour, shape, texture, size.
● Flower: colour of standard; colour of wing.
● Pod: length, including beak character, shape of transverse section (through seed).
● Seed: weight, size, shape, colour.
● Resistance to Bean Common Mosaic Virus, Bean anthracnose, Halo blight and Common blight.
(A detailed test guideline (012) is obtainable from UPOV; see Appendix 2.)
Soil pH and nutrition
Phaseolus vulgaris tolerates slightly acid soil conditions; soils with a pH 5.4–
6.5 can be used successfully. The general N:P:K ratio applied during seedbed preparation is 1:2:2. Gavras (1981) investigated the effect of mother plant min- eral nutrition on seed yield and quality and found that different ratios of nitrogen and phosphorus were required for relatively high seed yield and for seed quality.
Browning et al. (1982) reported the importance of a correct balance between nitrogen and phosphorus available to the plant for the production of high vigour seeds. Figure 11.2 shows the effects of three levels, each of phosphorus and nitrogen on the yield of bean seeds as determined by the cold test. The cold test was as described by Hampton et al. (1995).
Irrigation
Literature reviewed by Salter and Goode (1967) indicated that water shortages during anthesis and pod development seriously affected bean yield. Work in European temperate regions showed that irrigation applied before the start of anthesis only increased vegetative growth. However, as discussed by Davis (1997), early moisture stress, at the two trifoliate leaf stage can have a detri- mental effect on growth and affect flower initiation resulting in uneven crop maturity. There are many bean production areas where early and sustained irrigation is necessary to obtain a satisfactory crop.
Sowing
Seed of the bush types is sown in the late spring when the possibility of frost has passed and soil temperatures have risen sufficiently for satisfactory germination and plant growth. In some specialized areas in North America, notably Michigan, where length of season allows double cropping, seeds of early-maturing cultivars are drilled into the stubble of a previous barley crop or immediately after the stubble is ploughed in. When this technique is adopted seeds of early-maturing cultivars are drilled in early July.
The sowing rate depends on the relative seed size of the cultivar but is approximately 100 kg/ha for the bush types and 50 kg/ha for the climbing types. Bush cultivars are sown in rows 45–90 cm apart, according to cultivar and stage of multiplication. The climbing cultivars are sown in rows 90–120 cm apart. In some tropical areas cane frames or supports are erected, although generally they are supported by strings.
Flowering and pollination
Most cultivars of each type (i.e. bush and climbing) are day-neutral although there are some short-day cultivars in each group. The physiology of Phaseolus beans, including induction of flowering, pollination and pod growth has been reviewed by Davis (1997).
Fig. 11.2. Effects of three phosphorus and three nitrogen levels on seed yield and seed vigour in Phaseolus vulgaris.
10 20 30 40 50
Seed yield (g/plant)
60
N2 N3 N1
N2 N3 N1
3 P
2
1 1 2 3 P
5 10 15
Cold test Seed yield
Survival (%)
The flowers are self-compatible and are predominantly self-pollinated although some cross-pollination occurs. The degree of cross-pollination prob- ably increases in the tropics where insect activity (including thrips) is greater (Drijfhout, 1981).
Isolation
Many seed authorities stipulate a minimum distance of 3 m between a seed crop and any other crop of Phaseolus vulgaris. However, 50 m for seed crops in the final multiplication stage and 150 m for a crop intended for basic seed are preferable isolation distances.
Roguing stages
1. Before flowering: check plant habit, vigour and height according to type;
check foliage, leaf shape and colour.
2. At onset of flowering: check plant vigour and flower colour; remove plants showing symptoms of seed-borne pathogens.
3. Seed set and first pods formed: check pod characters, including shape and colour; remove late flowering off-types and plants showing symptoms of seed- borne pathogens.
Basic seed production
A scheme for maintaining breeders’ stocks of beans has been described by Drijfhout (1981). For basic seed single plant selections are made from a rela- tively large plant population grown from breeders’ stock seed. The selections are based on five successive inspections commencing immediately after seed- ling emergence. Particular care is taken to retain only seedlings with appropri- ate cotyledon colour. The young plants are then inspected a second time to remove plants which show inappropriate leaf characters. The third selection is made just prior to flowering in order to confirm the general plant form, height and earliness.
When flowering commences, the plants are examined a fourth time to check flower colour, and off-types are again removed. The fifth selection is made when the pods are developing and characters such as pod shape, length and colour can be seen, and other characters such as stringlessness can be detected. Plants showing symptoms of seed-borne pathogens are discarded at each stage of selection.
The remaining plants are harvested singly and low yielding plants (as deter- mined by seed yield) are rejected. The remaining seeds from selected plants are sown the following season as single plant selections and undesirable lines are rejected. The remainder are bulked for further multiplication and used as basic stock.
Harvesting
The dwarf or bush types are generally considered to be ready for a once-over harvest when the earliest pods are dry and parchment-like, and the remainder of the pods have turned yellow. The seeds’ moisture content at the time of harvesting should be between 20 and 25%; seed maturity is confirmed by opening sample pods, wherein the seeds should be fully developed with a mealy texture. Under good growing conditions the flowers tend to set until relatively late in the season. This leads to a loss from ‘shattering’ of the earliest mature seeds if harvesting is delayed. Smith (1955) examined the effects of stage at harvesting on bean seed yield and quality and found that there was a reduction equivalent to 358 kg/ha in harvested seed when the crop was cut before the earliest pods were fully mature. Figure 11.3 shows dwarf bean plants with mature seed pods prior to harvesting.
The plants are cut and placed in windrows for further drying before either combining or threshing, or they are combined direct from the standing crop.
The entire operation is planned to ensure both the minimum loss from shatter- ing and the least possible mechanical damage to the seeds which are especially susceptible to cotyledon cracking.
Fig. 11.3. Dwarf bean plants with ripe pods prior to cutting and harvesting.
The climbing cultivars mature over a longer period than the bush types so they are harvested by hand on three or more successive occasions as the older pods mature, or the plants are pulled out and dried off in windrows.
Threshing
Small quantities of seed are threshed by hand to avoid subsequent loss due to mechanical damage; this is especially important with small seed lots of basic or stock seed. Large seed lots are threshed with a drum speed of 250–350 rpm at a concave clearing of c.12–20 cm. The seeds’ moisture content should not be too low or excessive mechanical damage occurs during machine threshing.
Wilson and McDonald (1992) have evaluated six systems for the thresh- ing of Phaseolus vulgaris and found that the highest quality seed was pro- duced by open flail threshing or hand shelling. They concluded that, where feasible, manual threshing methods are superior to mechanical methods for small seed lots. Manual threshing would be expected to minimize cotyledon cracking.
Seed yield and 1000 grain weight
The seed yield is c.1500 kg/ha although under ideal production and harvesting conditions yields are c.2000 kg/ha.
The 1000 grain weight for Phaseolus vulgaris is c.250 g, although this can be up to 600 g in the smaller seeded cultivars.
Pathogens
The main seed-borne pathogens of Phaseolus species are listed in Table 11.2.