|Samac, Deborah - Debby|
Submitted to: Alfalfa Improvement Conference Proceedings
Publication Type: Abstract Only
Publication Acceptance Date: 7/17/1997
Publication Date: N/A
Technical Abstract: Alfalfa (Medicago sativa) populations with antibiosis-based resistance to the root-lesion nematode (Pratylenchus penetrans) have been developed by recurrent phenotypic selection. Individual plants that support significantly lower nematode reproduction were identified for molecular and biochemical characterization of defense responses. Before nematode infection, RNA blot analysis revealed 1.3 to 1.8-fold higher phenylpropanoid pathway mRNA levels in roots of resistant plants as compared to susceptible plants. Following nematode infection, phenylpropanoid mRNAs declined over 48 h in resistant roots. In susceptible roots, phenylpropanoid mRNAs rose during the first 12 h after infection and then declined. Acidic beta-1,3-glucanase mRNA levels were initially similar in both root types but accumulated more rapidly in resistant than in susceptible roots after infection. Levels of a class I chitinase mRNA were similar in both root types. Six h after cutting roots a marked increase in alfalfa trypsin inhibitor (ATI) mRNA levels was observed in response to wounding. In resistant inoculated roots, ATI mRNA levels were 1.4-fold higher than non-inoculated roots at 6 h and remained higher than control roots thereafter. In susceptible roots, nematode infection had no effect on ATI mRNA levels. Roots of both resistant and susceptible plants had similar constitutive levels of total isoflavonoids and nematode infection had no effect on isoflavonoid levels. Constitutive levels of medicarpin were highest in roots of the two most resistant plants, while one resistant plant had low amounts of medicarpin. Purified medicarpin incorporated into an agar medium inhibited nematode motility.