Reading Comprehension

PT7 · S3 · P3 · Q18 Crop Bacteria

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Cultivation of a single crop on a given tract of land leads eventually to decreased yields.

Topic

Using bacteria — including genetically altered ones — to suppress plant pathogens and improve crop yields.

Framework

Present Debate. The author lays out the technique, walks through the genetic-alteration extension, and presents proponents' and opponents' arguments before closing with a hopeful note.

Main Point

Beneficial soil bacteria like Pseudomonas fluorescents already improve crop yields by suppressing pathogens; proponents argue genetic alteration of bacteria could extend these benefits, while opponents worry about deliberate release. Proponents counter that specific alterations (like removing the frost-damage gene from P. syringae) make the altered strain safer than the original.

P1: Beneficial bacteria suppress pathogens

Continuous cultivation increases harmful soil bacteria; rotation breaks this. Even without rotation, soils become "suppressive" — partly because bacteria like P. fluorescents outcompete the pathogens. Treating wheat (and sugar beets, cotton, potatoes) seeds with these bacteria increases yields.

P2: Genetic alteration as the next step

Proponents suggest genetically altered bacteria could be even more useful — for example, releasing nonpathogenic P. syringae to crowd out the frost-damage variety. Opponents object to large-scale releases of altered bacteria. Proponents counter that the alteration is just removing the gene for frost damage, making the strain safer than the original.

P3: Even more ambitious uses

Some proponents go further: combining traits from different bacteria (e.g., transferring insecticidal-compound genes into corn-root pseudomonads). Such bacteria are hard to develop and may struggle in natural soil. Still, proponents see excellent prospects, and many hope risk-assessment efforts will satisfy opponents and let research go forward.

18.

It can be inferred from the passage that crop rotation can increase yields in part because

moving crop plants around makes
Out of Scope
Out of Scope: hardier / resistant to disease The passage doesn't say that moving crop plants makes them hardier (i.e. tougher / better able to withstand adversity). It just says that the parasitic bacteria that builds up in the soil is denied a suitable host when you remove one plant and replace it with a different type. When we move our corn from Field A to Field B, we're not making the corn plant tougher and more resistant to disease. We're just removing the corn from soil where parasitic organisms had built up, and planting it in soil that doesn't have parasitic organisms that want to use corn as a host.
18% picked this
the number of Pseudomonas fluorescens
Out of Support Window: Pseudomonas
The passage never connects the act of crop rotation to the number of Psuedomonas fluorescens. The passage actually seems to be saying the opposite. If you don't rotate crops, then the parasitic bacteria increases in the surrounding soil. And once that population grows, you can see within a number of years an increase in the number of beneficial bacteria like Pseudomonas fluorescents, which attack the parasitic bacteria.
10% picked this
the roots of many crop
Out of Scope: roots produce compounds
Nothing in our Support Window says anything about the roots of crop plants producing compounds. It says that harmful phytopathogens build up in the soil around the roots of our crop plants (that's why we've got to rotate these crops to another field, where those harmful parasites won't be found).
4% picked this
the presence of phytopathogenic bacteria
Too Strong: majority
Nothing in those first few sentences would support this strong claim that more than 50% of plant diseases are caused by the presence of phytopathogenic bacteria.
7% picked this
Correct
phytopathogens typically attack some plant
Why this is right
This is our best match for the available Support Text. We were told that crop rotation can cure the problem of "harmful phytopathogens building up in the soil surrounding the crop plants' roots" because it denies the pathogen a suitable host for a period of time. We're taking our corn out of Field A (where harmful phytopathogens have built up in the soil) and moving it to Field B (where these pathogens are absent or in lesser number). Meanwhile, we're rotating some other crop into Field A (we're taking strawberries away from Field B and rotating it into Field A). If phytopathogens usually found all plant species to be suitable hosts, then crop rotation wouldn't solve any problem. We would plant berries in Field A, and the corn-pathogens would start attacking the berry plants. The passage is saying that "berry plants are not a suitable host to corn-pathogens" (and similarly, berry-pathogens that have built up in Field B will not attack the corn we just moved to there). So we can tell that these pathogens are only going to be able to attack certain plants. They find other plants to be unsuitable hosts.
Skill tested: Inference · how this choice captures the passage's function is the move to repeat next time.
61% picked this

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