PLSCS 2110 Exam 2

Describe the steps in mass selection.

(1) A group of diverse plant lines are bulked and intermated, 2) in the next generation the progeny are evaluated and the best ones (perhaps 5%) are selected, 3) these selected plants are intermated, and (3) this selection is repeated through several more generations until the desired high performance crops are realized.

What three factors form the basis of Mendelian genetics?

(1) Alleles, (2) Law of Segregation, and (3) Law of Independent Assortment.

Name at least one general tillage guideline

(1) Avoid tillage when the soil is too wet or too dry, (2) retain as much surface residue as practical for crop grown, weed pressure, and other conditions, and (3) cultivate no deeper than needed to control weeds.

What two traits in weeds make them highly successful? Provide an example of each trait.

(1) Competitive - rapid growth, tall, rapid absorption of soil nutrients, and deep rooting for water. (2) Effective dispersal - underground structures, prolific seed production, and seed dormancy.

Name several factors that makes predicting soil nitrogen availability difficult.

(1) Dynamic cycling affects plant-available N (mineralization and denitrification), (2) weather (rainfall and temperature), and (3) varying plant needs for N over a growing season.

List three goals of tillage and explain explain how each of helps improve the crop system.

(1) Incorporation of residue (helps to control diseases and insects), (2) incorporation of manures, fertilizers, and lime (helps to ensure that added nutrients are not eroded away and cations are bound to soil in available forms; helps stimulate lime reaction with soil, and mineralization of organic matter), (3) weed control (cuts and buries plants to prevent competition, encourages seed germination early so weeds do not appear later), (4) preparation of seedbed (provides a uniform, smooth surface for accurate depth of planting, and achieves a firm soil and seed contact), and (5) alteration of soil physical properties (reduces compaction).

Name a limitation of genetic transformation.

(1) It is only feasible for a relatively small number of genes at a time and (2) it is used for traits that need just one or a few genes like herbicide and insect resistance.

List two ways that having a cover crop during winter months is advantageous.

(1) It prevents erosion, (2) the crop absorbs soil nitrogen (esp. NO3) thereby preventing N leaching, (3) the crop can suppress weeds, and (4) legumes fix N2.

Give an example of at least three complementarities in polyculture systems.

(1) Legume - non-legume and nitrogen, (2) deep-rooted and shallow rooted plants for water and nutrient efficiency, (3) in forages, varying growth patterns over a cropping season due to seasonal weather or moisture and corresponding differences in species adaptation, (4) tall crops with erect, vertical leaves and short crops with horizontal leaves, (5) insect and disease pest control by harboring beneficials, and (6) provision of an ecosystem service

Three sources of mineral nutrients are (1) Soil organic matter, (2) atmosphere, and (3) soil minerals and carbonates. Describe what mineral elements are provided by each.

(1) Soil organic matter provides N, S, P, and micronutrients, (2) the atmosphere is a source of N for biological fixation of N2 in legume nodules and NH3 and SO2, and (3) weathering of minerals and carbonates provides K, P, Ca, Mg, and micronutrients.

What is one property that affects nutrient availability? How does is affect it?

(1) Water (mobilization of nutrients), (2) temperature (roots and microbial functioning), (3) reduced (not oxidized)/flooded soils (more Fe, Mn, P available, and less S, Zn; and N is generally lost due to NO3 leaching or denitrification to N2 and N2O and loss to the atmosphere), and (4) soil pH (root function and nutrient availability).

Name at least two cultural practices for weed control.

(1) high crop population density, (2) cover crops, (3) companion crops, and (4) crop rotation.

Name at least three advantages of no-till systems.

(1) minimizes soil erosion, (2) maintains soil aggregates, (3) prevents excess aeration of soil thereby preventing excess microbial oxidation of soil organic matter to CO2, (4) improves soil water infiltration, (5) conserves tractor energy, and (6) can reduce the capital costs associated with tillage equipment used in conventional tillage

Name the three forms of mineral nutrient acquisition by plants.

(1) root uptake (by far most important), (2) direct uptake by leaves (foliar sprays), (3) gaseous forms of N (N2 which is fixed in legume nodules), NH3 can enter through stomata (a very small amount and only in special circumstances such as down-wind of a pig farm), and SO2 (also rare, and potentially damaging)

How many seeds will a typical redroot pigweed produce? How long can these seeds remain viable?

100,000 seeds. These seeds can remain viable for approximately 40 years.

How does the herbicide 2,4-D kill weeds?

2,4-D works as a chemical analog of the plant hormone auxin. To kill weeds, the dose of 2,4-D is sufficiently high that it overwhelms the plant system, causing extreme growth, deformity, and growth distortion which ultimately leads to the weed's death.

How many types of spores does black stem rust of wheat have in its full life cycle?

5

Define cropping system.

A cropping system is a set of crops grown on a farm, and the way they are arranged over space and time.

What does a cultivar mean in the context of plant breeding?

A cultivar is a plant selected through plant breeding processes and has gone through the rigorous testing phase successfully indicating its readiness for release.

What is the optimal soil pH?

A pH between 6 and 7.2.

What is a farming system?

A system characterized by the combination of different crops and livestock species that are produced on a farm

List at least two advantages and two disadvantages of herbicides in weed control.

Advantages include high weed toxicity (effectiveness in killing weeds), can be persistent over the entire season, selectivity even if the crop and weeds are intermingled, and economical when compared to other alternatives. Disadvantages of herbicides include health and safety concerns, can kill nontarget species, herbicide resistance through selection pressure means that herbicides and crops should be rotated and new ones developed, and they can be costly.

List two advantages of more diversity of crops and livestock on a farm. On the other hand, list at least one advantage of specialization.

Advantages of crop and livestock diversity include: (1) less risk to uncertain market prices, (2) less risk to stressful weather, and (3) spread labor demands to broader timeframes. The advantages of specialization include: (1) more efficient use of specialized equipment and (2) the knowledge and expertise needed is for a more manageable number of topics.

Name at least one advantage and one disadvantage from: a) fall plowing and b) spring plowing.

Advantages of fall plowing include: (1) breakdown of crop residues during the winter, (2) faster warm-up of soil in the spring, and (3) less work for farmer in the spring. A disadvantage of fall plowing is that the soil is more vulnerable to erosion and nutrient loss. The advantage of spring plowing is that in winter it leaves more crop stubble on the soil surface and does not disturb rootsoil aggregates thereby reducing erosion, but a disadvantage is that it delays tillage and planting until soil moisture drains in the spring.

Which leguminous plant species can produce upwards of 200 pounds an acre of nitrogen?

Alfalfa, red clover, especially in stands two or three years after establishment.

What two chemical nitrogen fertilizers are sensitive to moisture?

Ammonium nitrate and urea are hygroscopic (absorb moisture from the air)

What is an alternate host?

An alternate host is a second plant species that can be integral in the lifecycle of certain fungi. Example: in black stem rust., wheat is the first host and barberry is the alternate host.

Name one annual and one perennial weed that is common in New York State.

Annual weeds - velvetleaf, pigweed, lambsquarters, and ragweed. Perennial weeds - Canada thistle, nutsedge, barnyardgrass, quackgrass, and bindweed. (many others could be mentioned)

How does atrazine kill weeds?

Atrazine is taken up by foliage or roots (then transported to leaves) and in the leaves it blocks photosynthetic electron transport, thereby killing leaf tissue.

What is backcrossing?

Backcrossing is a plant breeding technique used to introgress a desired trait from a source parent into a plant cultivar lacking this trait but with other desirable qualities. The technique refers to repeated crossing of the offspring of the two crossed lines to the recurrent parent which is highly desirable though lacking the new trait. Molecular markers can help speed up the process by identifying which of the many progeny still have desired introgressed gene(s) and which have the greater proportion of the recurrent parent for all other parts of the genome.

In well-aerated soils, bacteria will convert NH4 to what form? What is the name of this process?

Bacteria will convert NH4 into NO3 in a process called nitrification

Name at least three types of plant pathogens.

Bacteria, viruses, fungi, oomycetes, nematodes, and parasitic plants.

Name the forms of nitrogen inputs in the Nitrogen Cycle.

Biological fixation, lightening conversion of N2 to fixed N in the atmosphere, industrial fixation of N2 to NH3, manure, and plant recycling (soil organic matter).

Describe the difference between continuous cropping and crop rotation. Give an example of each.

Continuous cropping implies that the same crop is grown for two years or more on the same plot of land, whereas crop rotation is the sequence of different crops grown over several years on the same land. An example of a continuous cropping system would be corn-corn-corn, etc. and examples of crop rotation are corn-soybean-corn. Some systems that involve continuous sequences of a crops, such as corn-oats-alfalfa-alfalfa-alfalfa, is considered desirable because the alfalfa is a perennial sod crop that suppresses soil erosion, fixes N2 (legume), and does not require intense pesticide or fertilizer inputs.

Conventional tillage has how many steps? What type of tool(s) is used at each step?

Conventional tillage has two or more steps - primary tillage, secondary tillage, and finishing. The main tool used for primary tillage is a moldboard plow and in secondary tillage, harrows (disk and field cultivator) or tine and drag finishers are used.

Why was the adoption of genetically engineered herbicide resistant crops much later for corn as compared to other crops?

Corn had many reliable alternatives prior to genetically engineered herbicide tolerant varieties, unlike soybean and cotton, which did not have better alternatives.

Name the three types of perennial weed underground dispersal structures.

Creeping root system, tubers, and rhizomes.

Name three advantages of crop rotation systems.

Crop rotation advantages over continuous cropping include weed control, disease and insect control, increased soil fertility and quality, reduced soil erosion, and rotation effects. However, the number, type, and sequence of crops in the rotation can influence these advantages.

Hybrid production is common for what kinds of crops?

Crops that are highly cross-pollinating and exhibit a lot of hybrid vigor (heterosis), such as corn and some vegetables.

What happens to denitrification rates as soil temperature increases under watersaturated conditions?

Denitrification rates increase in warm soils and the rate of nitrogen loss from the soil increases compared to the rate in cooler conditions.

In general, what are plant 'essential' elements?

Essential elements are those elements that are critical to crop metabolism and are needed by the plant to complete its life cycle.

Why might farmers grow crops in a monoculture rather than a polyculture?

Farmers are likely to grow crops in a monoculture due to ease in management, competition and poor performance when two crops are grown together, and the strong market value of certain crops relative to others.

What happens to soil nitrogen when soils are flooded?

Flooding creates hypoxic (reducing) conditions where denitrification by soil microorganisms converts NO3 to gaseous forms (N2 and N2O), and nitrogen is then lost to the atmosphere.

Give an example of one of the most serious fungal diseases in wheat in the world?

Fusarium head blight (especially in wheat), and stem rust of wheat

What are two other names for genetic transformation?

Genetic engineering or genetically modified.

What are the two most commonly used herbicides?

Glyphosate and atrazine.

How does glyphosate kill weeds?

Glyphosate is sprayed on foliage, then is transported to growing points where it block the enzyme EPSP synthase which is needed for aromatic amino acid synthesis. This kills the growing points and the plant dies.

What is Liebig's Law of the Minimum?

Growth of a crop is not determined by the total amount of resources available, but rather by the scarcest available resource or nutrient.

Define herbicide selectivity.

Herbicide selectivity refers to the relative sensitivity for killing a target weed population compared to harming the field crop.

Why is herbicide usage for wheat only about half as much as that of other crops?

Herbicide usage is lower in wheat because wheat is generally planted in narrow rows at high densities making it more competitive with weeds for resources like light and water. Also, in the water-limited wheat-growing areas weeds are also less competitive (given water limit) and farmers need to limit costs given low yields.

List three control methods for weeds in crops.

Herbicides, tillage and mechanical means, and biological approaches.

Describe the range of products produced from a dairy farming system.

Milk from dairy cattle; meat from sale of old cows and from bull calves and steers, and a variety of products fed to cattle: alfalfa, corn, oats, and pasture.

Explain the phenotypic ratios 1:1 and 3:1 using green and yellow pea plants as an example.

In a 1:1 phenotypic ratio with pea plants and a single dominant gene controlling the trait, offspring are a result of a cross between a heterozygous parent and a homozygous recessive parent. The offspring are equally as likely to be either heterozygous dominant (green) or homozygous recessive (yellow) (e.g. Gg or gg). In a 3:1 ratio, offspring are a result of a crossing between two heterozygous dominant parents. The offspring are three times as likely to be green, either heterozygous or homozygous dominant, than they are homozygous recessive.

For the United States, list the relative order of importance of plant pathogens.

In order, from most important to least important: fungi, oomycetes, bacteria, and viruses. (this order is debatable depending on the host plant species, but note the contrast with human pathogens where fungi and oomycetes are of much lesser importance)

What are two forms of mechanical weed control?

In-season tillage (cultivation) and mowing (generally for pastures).

What happens when plants are continually self-pollinated for several generations?

Inbreeding depression occurs with these plants and they lose their hybrid vigor.

What are some goals of plant breeding?

Increased yield, disease and insect resistance, quality traits (i.e. forage digestibility, fruit color/flavor, etc.), ease of harvest, and persistence/winter hardiness.

Name two of the mineral micronutrients that are common in human micronutrient malnutrition.

Iron, zinc, iodine, calcium, selenium.

What nutrients does the plant generally take up during its vegetative period? During season-long uptake?

Minerals taken up primarily during the vegetative period include nitrogen, potassium, and magnesium, whereas phosphorus, sulfur, and zinc are taken up during the entire growing season.

What are symptoms of fungal infection?

Leaf spots, blights, wilts, rots, and cankers

Why would plant breeders use marker-assisted methods over genetic modification (GM) methods or vice versa?

Marker-assisted methods are ideal for when the desired trait is already present in some individuals in the current population. GM, however, may be desirable when there is a particular gene not present in a population.

What is the key to developing new genetic combinations?

Meiosis and associated independent assortment and crossing over. Such processes occur in the formation of the gametes that are in the egg and sperm, and their joining together in fertilization.

What contributes to dietary micronutrient malnutrition?

Micronutrient malnutrition is a result of a narrow diets that lack good sources of all the needed micronutrients, but can also be due to soil deficiencies, which leads to poor nutrient content of crops consumed.

In general, what role do micronutrients have in plants?

Micronutrients are essential constituents in numerous enzymes and other biologically active components or are the key factors to activating enzymes

What is the general tillage guideline for conservation tillage?

More than thirty percent of crop residue must be left undisturbed by tillage.

What are general deficiency trends in alkaline soils?

Most micronutrients with the exception of Mo and P are generally deficient.

What form of nitrogen do legume nodules (the rhizobium bacteria therein) produce internally?

NH4

What are the main forms of nitrogen taken up from the soil by plants?

NH4 and NO3

N is a component of which plant constituents?

NH4 assimilation is the first step in synthesis of amino acids, proteins, DNA, and RNA among others.

Which is less likely to be leached from soil, NO3 or NH4? Why?

NH4+ is less likely to leach from soil because it is positively charged and held in contrast to NO3 (negatively charged) by the cation exchange capacity (CEC) of soil.

In traditional plant breeding, how do repeated rounds of selection lead to improved genetic combinations?

New genetic combinations are formed with repeated crossings and in each cycle of selection breeder's rouge out less desirable germplasm and focus further improvement on superior germplasm.

What is the most prevalent macronutrient in a plant?

Nitrogen

Describe the visual appearance of nitrogen deficiency in corn.

Nitrogen deficiency in corn usually presents itself as a yellowing which begins along the midrib of the leaf and forms a 'v' shape with the widest section of yellowing at the tip then narrowing to the leaf's midrib. Leaf margins remain green except toward the tip of the leaf. Older leaves (lowest on the plant) generally show nitrogen deficiency first.

In general, most corn planted in the United States is under continuous cropping?

No, according to the USDA, more than three quarters of the corn in the U.S. is planted with crop rotation.

What is the most recent tillage trend in the United States? Is this trend common in the Northeast and why?

No-till has increased in recent years, especially in the midwest and southeastern states. No, this is not a popular trend in the Northeast because tillage is considered useful in colder northern regions by exposing dark soil to solar radiation thereby warming up soils before planting.

What has an effect on both crop quality and human/animal nutrition?

Nutrients

What are plant pathogens?

Plant pathogens are living organisms that cause disease in plants.

What benefits do plants provide to rhizobia and vice versa in their symbiotic relationship?

Plants provide carbon nutrition and a low oxygen microenvironment for bacteria whereas the bacteria are able to convert atmospheric N2 to NH4 for plant use.

What is the goal of secondary tillage? Is there a risk with secondary tillage?

Secondary tillage aims to prepare the seedbed by settling and smoothing soil. The risks associated with this type of tillage is that it increases chances of breaking up soil aggregates that are valuable in maintaining soil porosity and the extra tractor traffic increases soil compaction

What is a common indicator of phosphorus deficiency in plants?

Red to purplish color on the leaves.

What are saprophytes?

Saprophytes are organisms that live on dead plant tissues; they do not have active structures or mechanisms to infect and invade hosts as parasites usually do, but they result in disease by taking advantage of infection sites then spreading to surrounding tissue of the plant.

Name an example of a self-pollinated species, a cross-pollinated species, and a vegetatively propagated (clonal) plant species.

Self-pollinated species include rice, wheat, and soybean; a crosspollinated species is maize; a vegetatively propagated crops include sweet potato, sugarcane, cassava, and potato.

List the two types of nitrogen testing that involve plant tissues.

Stem NO3 test and leaf green color test.

What is strip cropping?

Strip cropping is a quasi-polyculture system where crops are grown in monocultures in adjacent strips within the same field.

What is the name of the process that is used to form anhydrous ammonia (NH3) for fertilizer?

The Haber-Bosch process.

What is the deficiency symptom approach to fertilization? What is a problem with this approach in determining nutrient deficiency?

The deficiency system approach is a simple, no cost diagnostic based on identifying characteristic visual symptoms of nutrient deficiency. However, a problem with this approach is that symptoms can often be confused with nonnutrient stresses, like disease, drought, and flooding. Also, in addition to species differences, crop genotypes within a species can differ in their appearance when deficient.

Define the two types of multiple cropping systems

The first is double cropping where one crop follows another crop in a series during a particular cropping season (common in tropical and mild-winter climates), and the second is relay cropping where the second crop is sown before the first crop is harvested.

What were the advantages of John Deere's early plow?

The plow 1) was made of hardened steel that becomes polished by soil which scours the steel smooth and shiny to a low-friction surface; 2) had an ideal curvature that requires less energy, and 3) inverted the soil cleanly for thorough coverage of crop residue.

What crops are typically grown in monocultures?

The preponderance of annual crops grown in temperate and tropical regions are grown as monocrops in a particular season. This is true for grains, fruits, and vegetables. Forage crops are more often polycultures, as are agroforestry and manually-cultured gardens

Name three macronutrients and three micronutrients essential to plants.

There are at least 14 essential mineral nutrients. Macronutrients include - nitrogen, potassium, phosphorus, calcium, magnesium, and sulfur. Micronutrients include - iron, manganese, copper, molybdenum, zinc, boron, nickel, and chlorine.

What is the difference between a field cultivator and a chisel plow? What are these tools used for today?

There is no fundamental difference between a chisel plow and a field cultivator; they are both names for the same tool. Today, these tools are used more and more in primary tillage as opposed to its past use as a post planting tool for removing weeds. Choice of shank and sweep type, and depth of use, determine the tool's action in the soil.

Give two examples of how roots take up nutrients

Uptake through membranes in roots is via (1) active uptake against a chemical gradient, (2) passive down-hill diffusion through protein channels in membranes, (3) uptake of complexes of the mineral nutrient (such as iron) with organic acid exudates, and (4) uptake by mycorrhizae which in turn transfer the nutrient to the root. Transport from the soil to root surface is in the soil solution by (1) Mass flow, (2) diffusion, and (3) through mycorrhizae to root via

List the losses of nitrogen from the terrestrial zone (soil) in the Nitrogen Cycle.

Volatilization, denitrification, and leaching.

How are seeds dispersed?

Weed seeds are dispersed through water, wind, animals, and human activities (eg. Machinery).

Define the Law of Segregation

While plants are diploid and have two copies of each gene, from each parent, offspring receive one copy of each gene via gametes (haploids).

Name one challenge and one advantage to growing crops in a polyculture.

a. Challenges to growing crops in a polyculture include i. balancing populations of competing crops ii. different optima for nutrients, weed, controls, and tillage iii. difficulty for mechanical tillage/planting harvest of multiple crops iv. poor complementarity of crops b. Advantages of polycultures are i. yield stability (responses to weather, pests, etc.), ii. better use of resources due to complementarity. iii. Control of soil erosion and weed suppression (cover crops).

What is the name of the filamentous threads that compose fungi?

hyphae, which are microscopic, threadlike filaments of cells; mycelium is the structure when the hyphae form a larger, macroscopic structure

What damage does fusarium head blight cause in addition to decreasing wheat yield?

it produces a compound in the infected grain that is toxic to animals: vomitoxin, a mycotoxin.

Acidic soils are generally below what pH range?

pH < 5.5.

In in the full fungal life cycle, why is the meiosis stage important for developing future epidemics?

while crop plants can be bred for resistance to current strains, genetic recombination during meiosis can create new fungal strains for which crop plants do not have resistance.