Vegetable Science Quiz 2

  1. Onion
    How does temperature affect bulbing?
    • Bulbing initiation is controlled by daylength and promoted by high temperatures.
    • Favoring mean monthly temperatures between 55 and 75°F during the early stages of growth before bulbing.
    • Once bulbing is initiated, warm temperatures promote rapid growth, while cool temperatures will slow the bulbing response
  2. How does daylength affect bulbing? Are onions long, short or day-neutral plants? Why does the industry refer to "short, medium and long-day" onions?
    • Bulbing initiation is controlled by daylength
    • It is an obligate long-day plant
    • Long day (14-16 hours; optimal latitudes of 37-42°N)
    • Medium day (13-15 hours; optimal latitudes 35-38°N)
    • Short day (12-14 hours; optimal latitudes 32-35°N, with a maximum of 36°N)
    • Medium and short day designations are                                               misnomers
  3. What would be the effect of planting onion seed from New York in Southern Miami? The effect of planting seed from Southern Miami in New York?
    • New York planted in South: it will remain vegetative as critical daylength will never be exceeded.
    • Southern is planted in New York: it will produce a small bulb as the critical daylength will be exceeded early in the plants growth
  4. How does size relate to the ability of the onion plant to sense day length?
    Onions in the field need to be of a certain size before they can sense the day length
  5. What temperatures induce the quickest bolting response in onion? Why do cooler and warmer temperatures result in a slower response or no response at all?
    Most rapid bolting is induced by temperature between 40 and 45°F, but responses occur between 40-50°F.
  6. At what size does the onion plant begin to sense cool temperature?
  7. In what ways are onions classified? What are the general characteristics of onions destined to be dehydrated (processing type).
    • 1. By daylength response
    • -Short day onions: winter in south and CA for immediate consumption
    • -Medium-day onions: valley, globe shaped, must be resistant to bolting
    • -Long-day onions: Derivatives of Sweet Spanish
    • 2. By pungency
    • 3. By use
  8. Why are muck soils considered to be better than mineral soils for onion growth?
    • have lots of organic matter
    • can absorb 20x its weight in water
    • loose soil that results in pretty roots
    • easy on equipment
    • dark soil
  9. What is the definition of a "muck" soil?
  10. ]Muck attributes:
    a) What are the advantages of growing vegetables on a muck soil?
    b) What is the greatest disadvantage, i.e., what exactly is subsidence?
    c) What factors cause subsidence?
    d) How can the process of subsidence by slowed?
    • Disadvantages: organic matter decomposes with heat and oxygen-> subsidence (direct oxidation by oxygen or microbial digestion)
    • can be sticky and is hard to wash off products
    • they are short time and have a limited life
  11. Are onions shallow, moderately deep-rooted, or deep-rooted?
    • Onions are a shallow rooted crop
    • 1.5 to 2.0 feet, though most water extraction is from the top 12 inches of soil
    • as the plants are shallow-rooted, frequent irrigation will be necessary
  12. How does excess nitrogen affect bulbing? A nitrogen deficiency?
    • Nitrogen deficiency increases bulbing 
    • Excessive nitrogen delays bulbing
  13. What are the common diseases of onions?
    • Downy mildew: portion of leaf brown. causes fields to not be green but have a yellow color.
    • Purple Blotch: destroys the tissue
    • Pink Root: Infects and kills onion roots, causing stunting of plant. Smaller bulbs with pinkish roots-reduces the vigor.
    • White rot and Fusarium basal rot: together with pink root, are common serious root and bulb diseases during production
    • Neck rot, black mold and blue mold
  14. What is a common pest of onions in California, one that uses rasping mouthparts to eat leaf tissue?
    • ************
    • Onion thrips: most common and most serious
    • Onion maggots
    • Mites, seed corn maggot, leafminers and army worms
  15. When onion bulbs reach "maturation", the tops of the plants will fall over. When approximately 50% of the plant tops have fallen, the bulbs are undercut. What is undercutting and why are the bulbs undercut, i.e., how does undercutting benefit quality and yield?
  16. Why are onions cured -- what are the benefits? How is it usually accomplished in California? Why is it disadvantageous to overcure?
    • Cure onions so necks are not soft and bacteria can't enter. Causes decay at necks
    • To dry outer scales of onion and to complete drying of neck of bulb
  17. Irish and sweet potatoes are cured, too. How do the objectives of curing for these two commodities differ from the objectives of curing for onions? How exactly does curing affect the quality of sweet potatoes?
    • Curing involves placement of sweet potatoes at 85°F temperature, 90-95% RH for 4-8 days.
    • Curing of Irish Potatoes - Tubers cured at 60°F and 95% R.H. for 2 weeks
  18. What is the recommended storage temperature and relative humidity for onions? What will often happen to the crop if the storage temperature rises much above 32°F. What are the consequences if the relative humidity also goes too high?
    32°F, 60-70% RH
  19. What chemical has been successfully used to prevent the sprouting of onions and Irish potatoes? How and when is it applied? Why is green leaf tissue necessary for its successful use? What does this chemical do in the bulb or tuber?
    • Necessary to cure Irish potatoes. If infected it can ruin entire load.
    • Maillard reaction: Heat+Amino acids+sugar=pigment
    • meleic hydrazide use to prevent sprouting after harvest by stopping tissue development
  20. How long can one expect to successfully store good quality, pungent, globe onions if stored at 32°F?
    Globe onion can be held for 6-8 months at 32°F
  21. How long can one expect to successfully store good quality sweet onions if stored at 32°F?
    Sweet onions do not store as well as pungent onions.
  22. How does the storage ability of spring/summer onions compare to that of fall-harvested onions?
    Onions harvest in spring, early summer do not store as well as those harvested in late summer, fall
  23. Sweet corn is a monoecious plant. What structures support the male flowers, i.e., what are the male "flowers" called? An ear of corn is comprised of numerous ovaries with elongated styles. What name is commonly given to the elongated styles as they appear on the plant?
    The male flower of a corn plant is called the tassel, while the ear with its corn silk is the female flower.
  24. What is meant by saying a plant is dioecious? Gynoecious? Andromonoecious?
    • Monoecious: separated but on the same plant (1 house)
    • Dioecious: Separated but on the same plant (2 houses)
    • Gynoecious: female houses (cucumbers) all female flowers on same plant
    • Andromonoecious: male houses Male->male&female->female flowers left on vine
  25. Corn is a cross-pollinated crop. What is the agent of cross-pollination? What practical significance does the fact that sweet corn is cross-pollinated have for a farmer growing seed corn of a particular cultivar?
    • Cross pollinated by wind
    • Tassels shed pollen before stigmas become receptive
  26. What is the recommended isolation distance for an insect (bee) pollinated crop? Wind pollinated crop? Self-pollinated crop? What is an example of a wind-pollinated crop? Self-pollinated crop?
    • Maintain a distance of 250 ft. or greater between varieties (UCDavis recommends a minimum distance of 330 ft.
    • Plant varieties with 2 weeks or greater difference in time of pollination
  27. Sweet corn crossed with field corn yields what type of corn? White corn crossed with yellow, purple or red corn yields what color kernels? What is a possible consequence of crossing a supersweet corn variety with a regular (su) corn variety?
    • Sweet crossed with starchy (field corn) always ends up starchy
    • White crossed with yellow shows yellow
    • White crossed with purple gives purple
    • White crossed with red gives red
    • Need to separate fields of corn by appropriate distances if know that a potential cross can impair quality
  28. Is corn a shallow rooted, moderately deep-rooted, or deep rooted crop? What are "brace" roots? Are they important to the crop?
    The root system occurs primarily within the top 2 feet of soil and therefore, sweet corn is considered a shallow-rooted crop
  29. How are sweet corn cultivars classified, i.e., by what factors are sweet corn cultivars classified?
    • 1. Kernel color: yellow, white, or bicolor
    • 2. Earliness
    • 3. Use: fresh market, freezing,                       canning, or shipping
    • 4. Level of sweetness
    • 5. Degree-days to maturity
  30. Three genes were discussed that are involved in the sweetness of sweet corn, the su, se and sh2 genes. Which is the original sweet corn gene? How exactly does the se gene affect sweetness and the sugar to starch conversion, compared to corn containing only the su gene? How exactly does the sh2 gene affect sweetness and the sugar to starch conversion? (You do not have to memorize any tables; simply give the general effects of each gene.)
    • Original supersweet cultivar was 'Illini Xtra Sweet'
    • su gene (allele)    
    • se gene -- sugar enhancer     
    • “Shrunken 2” (sh2) gene
    • ****
  31. Sweet corn cultivars containing the sh2 gene have been classified as "supersweet" cultivars. What effect does this gene have on the appearance of corn seed? How does this gene affect the vigor of the seed? How are the seeds protected from insect damage and fungal rots?
  32. What is the base growth temperature for corn? for peas? for tomatoes? What does it mean to say that the corn, or any crop, has a "base growth temperature?"
    • Good growth is found in months with mean temperatures between 60 and 75°F
    • Best growth obtained with mean monthly temperatures of 68° to 72°F but a good range is considered to be 60-75°F.
    • Ideal temp for growth is 85-95 degrees
    • 50 degrees F for germination threshold temp
  33. How is a degree day calculated?
    • (high temp+low temp)/2 - 50. 
    • shorter degree days=earlier harvest
    • warm temp=fast growth
    • low temp=slow growth
  34. The degree-day system is used to determine planting dates and to predict harvest times for both corn and peas. What assumption underlies the use of this system, i.e., what is considered to be the relationship between growth rate and temperature for these two crops under normal field conditions?
  35. How is the degree-day system used to determine planting dates based on the desired days between harvests?
  36. How is corn normally planted in California, i.e., what are the normal beds widths, number of rows per beds and in-row spacings? Are vacuum (precision) seeders used when planting sweet corn? Does the seed need to be coated if used with a vacuum seeder?
    • Plant 3/4 to 1” deep for weak seed or seed being planted into cold and/or wet ground and up to 3” deep for late season plantings.
    • in-row spacing of 8-9” between plants
    • 36-40” beds, single row but some larger beds used (up to 66” with 2 rows/bed).
  37. How is sweet corn germinated after planting, i.e., what irrigation method has historically been important for this crop? What is the classic irrigation scheme for this crop? Is corn grown much nowadays with drip? What are potential benefits of using a drip system?
  38. Why is cultivation at lay-by so important for corn?
  39. Some crops are luxury consumers of nutrients. An example is sweet corn. What exactly does it mean to say that a crop is a "luxury consumer," i.e., what is luxury consumption? What practical economic effects does luxury consumption have for the farmer? What nutrient is thought to be especially important facilitating the development of sweetness in the kernels?
    • Luxury feeder for nitrogen
    • will absorb more than needs and stores in leaves. Has nice big stocks and leaves but will still will have 1 ear per stock
  40. What are the common insect problems of sweet corn?
    • Corn ear worms
    • Mites 
    • Corn root worms
    • Army worms 
    • Cut worms
  41. Corn rootworms are the larval form of what insect? How are corn rootworms controlled?
  42. What is corn smut? How does it affect kernel appearance? Are parts of the corn plant other the ear capable of being affected by this problem? How is this problem controlled?
    Most common in warm production areasResistant varieties availableFungus that swells up in the kernels full on blue and black spores
  43. What is hyperplasia? Hypertrophy?
    • Hyperplasia: the enlargement of an organ or tissue caused by an increase in the reproduction rate of its cell
    • Hypertrophy: Is the increase in the volume of an organ or tissue due to the enlargement of its component cells. It is distinguished from hyperplasia, in which the cells remain approximately the same size but increase in number.
  44. What causes corn earworm? How are they controlled? How does corn earworm affect marketability? In some areas with heavy infestations, what must be done in order market the ears? Is this normally done in California?
  45. What are the maturation stages of a kernel of corn? At what stage is it considered ideal to harvest sweet corn for fresh market? At what stage is it considered ideal to harvest sweet corn to make "cream" corn?
    • 1. Pre-milk
    • 2. Milk
    • 3. Pre-dough
    • 4. Dough
    • In north harvest at pre-dough to be canned(must be cooked)
    • Want to harvest at milk stage
    • Sugar content highest at milk stage
  46. What physical methods/instruments are used to determine when a field is ready to be harvested, i.e., when the ears are high in sweetness but still tender?
    • Approximately 21 days after the silks have appeared, the ears are ready for harvest.
    • Cool nights are particularly important at harvest time, slowing maturity and extending the time at which sugar content
    • Early morning harvest is recommended
    • Harvest dependent on visual appearance of husks
    • -Refractometer
    • -Succulometer
    • -Oven drying 
    • -Shear press
  47. What is refraction? What does a refractometer measure? Why is using a refractometer not the best method for determining corn sweetness?
  48. At what temperature/relative humidity should the ears be stored? How does the storage temperature for sweet corn, a warm season crop, differ from the storage temperature for other warm season vegetables?
    32°F and 95-98% RH
  49. What causes the denting of corn kernels?
  50. Uneven or incomplete kernel fill of ears may be caused by poor pollination or kernel abortion. What factors are associated with poor pollination? What factors have been associated with kernel abortion?
    Top of ear should have miniature kernels about 1/2 size, not "blanks".
Card Set
Vegetable Science Quiz 2
AEPS 190 Vegetable Science Quiz 2