Reproductive development

High temperature affects reproductive development in two ways, both of which potentially reduce yields. Firstly, the rate of reproductive development is accelerated, which shortens the seed-filling period and the fruit maturation period. Generally, this results in lower individual seed and fruit weights and in some cases reduced concentrations of soluble solids in the fruit. In addition, in many crops the reproductive events themselves are prevented at temperatures only a few degrees above optimal. Reduced fruit set in tomato (see review by Kinet and Peet, 1997) and pepper (Wien, 1997c and references cited therein) occurs as a result of high temperature. In pepper, fruit set was reduced at 27/21°C compared with 21/16°C and no fruit set occurred at 38/32°C (Fig. 10.5). In tomato, high temperatures after pollen release decreased fruit set, yields and seed set in tomato even when pollen was produced under optimal conditions (Peet et al., 1997). Overall, however, pre-anthesis stress appears to be more injurious than stress applied after pollen arrives on the

Table 10.3. Temperature demands and sensitivities of vegetable species. (From Krug, 1997.)

Temperature

Vegetable species

Frost sensitivitya

Hot - growth range 18-35°C; optimum range 25-27°C

Okra (Abelmoschus esculentus)

Roselle (Hibiscus sabdariffa)

Watermelon (Citrullus lanatus var. vulgaris)

Melon (Cucumis melo)

Capsicum species

Sweet potato (Ipomea batatas)

Warm - growth range (10) 12-35°C; optimum 20-25°C

Cucumber (Cucumis sativus)

Aubergine (Solanum melongena)

Sweet pepper (Capsicum annuum)

Pumpkin, squash (Cucurbita species)

New Zealand spinach (Tetragonia tetragonioides)

Maize (Zea mays)

Tomato (Lycopersicon esculentum)

Phaseolus species

Cool - hot - growth range (5) 7-30°C; optimum 20-25°C

Colocasia (Colocasia esculenta) Globe artichoke (Cynara scolymus) Onion, shallot (Allium cepa) Leek (Allium porrum) Garlic (Allium sativum) Chicory (Cichorium intybus var. foliosum) Pak-choi (Brassica chinensis) Scorzonera (Scorzonera hispanica) Chives (Allium schoenoprasum)

Cool-warm-growth range (5) 7-25°C; optimum 18-25°C

Pea (Pisum sativum) Broad bean (Vicia faba)

Cauliflower (Brassica oleracea convar. botrytis var. botrytis)

Broccoli (Brassica oleracea convar. botrytis var. italica)

Cabbage (Brassica oleracea convar. capitata var. capitata)

Kohlrabi (Brassica oleracea convar. caulorapa var. gongylodes)

Table 10.3. Continued

Frost

Temperature Vegetable species sensitivitya

Kale (Brassica oleracea convar. acephala var. -sabellica)

Brussels sprouts (Brassica oleracea convar. fruticosa -var. gemmifera)

Turnip (Brassica rapa subsp. rapa) -

Rutabaga (Brassica napus subsp. rapifera) -

Chinese cabbage (Brassica rapa subsp. pekinensis) -

Parsley (Etroselinum crispum) -

Fennel (Foeniculum vulgare) (+)

Dill (Anethum graveolens) (+)

Radish (Raphanus sativus var. sativus) (+)

Radish (Raphanus sativus var. niger) (+)

Red beet (Beta vulgaris convar. vulgaris) (-)

Swiss chard (Beta vulgaris convar. cicla) (-)

Spinach (Spinacia oleracea) -

Lettuce (Lactuca sativa var. capitata) (+)

Endive (Cichorium endivia) -

Carrot (Daucus carota) -

Celery, celeriac (Apium graveolens) (+)

Parsnip (Pastinaca sativa) -

Potato (Solanum tuberosum) +

Lambs lettuce (Valerianella locusta) -

Rhubarb (Rheum rhaponticum) -

Asparagus (Asparagus officinalis) (+)

Horseradish (Armoracia rusticana) -

Garden cress (Lepidium sativum) (+)

a+, sensitive to weak frost; -, relatively insensitive; (+)(-) uncertain.

stigma (Peet et al., 1998). This was shown in an experiment in which heat stresses of 27 and 29°C were applied separately to male-sterile and male-fertile tomato plants of the same cultivar. Male-sterile plants receiving pollen from heat-stressed male fertiles had very reduced or no fruit set, regardless of the growth conditions of the male-sterile. Growth conditions of the male-steriles (i.e. female flowers parts and conditions after pollination) appeared to be less critical for yield (Fig. 10.6). Reduced pollen release and impaired pollen function appeared to be the main factors accounting for yield and seed set reductions. The most sensitive period was 15 to 5 days before anthesis, and a duration of 10 days was required for an effect (Sato, 1998).

Other vegetables in which reproductive development is particularly sensitive to high temperatures include bean (e.g. Konsens et al., 1991; Davis, 1997) and cowpeas (Vigna unguiculata (L.) Walp. Subsp. unguiculata (L.) Walp.) (e.g. Ahmed et al., 1992). In pea (Pisum sativum L. subsp. sativum),

21/16 27/21 38/32

Temperature (°C)

Fig. 10.5. Influence of air temperature and soil moisture on percentage of fruit set of 'World Beater' pepper grown in pots in glasshouse compartments. Fruits were removed after setting. Data are averages of 2 years' experiments, 1932-34 (Cochran, 1936). (From Wien, 1997c.)

21/16 27/21 38/32

Temperature (°C)

Fig. 10.5. Influence of air temperature and soil moisture on percentage of fruit set of 'World Beater' pepper grown in pots in glasshouse compartments. Fruits were removed after setting. Data are averages of 2 years' experiments, 1932-34 (Cochran, 1936). (From Wien, 1997c.)

temperatures above 25.6°C during bloom and pod set reduce flower and pod number and yields (Muehlbauer and McPhee, 1997). In maize (Wolfe et al., 1997), warm temperatures can reduce seasonal productivity by accelerating developmental rates, shortening vegetative and reproductive growth phases, reducing leaf area duration and reducing ear quality (see Table 10.1 for details).

Was this article helpful?

0 0
Guide to Alternative Fuels

Guide to Alternative Fuels

Your Alternative Fuel Solution for Saving Money, Reducing Oil Dependency, and Helping the Planet. Ethanol is an alternative to gasoline. The use of ethanol has been demonstrated to reduce greenhouse emissions slightly as compared to gasoline. Through this ebook, you are going to learn what you will need to know why choosing an alternative fuel may benefit you and your future.

Get My Free Ebook


Post a comment