Cotton Germplasm: Root-Knot Nematode Resistance in Day-Neutral Primitive Accessions Jack C. McCarty, Johnie N. Jenkins, and Michael Robinson McCarty is a research agronomist, and Jenkins is the director of the USDA-ARS Crop Science Research Laboratory, which is based at Missississippi State University. Robinson is a former graduate research assistant in the MSU Department of Plant and Soil Sci ences. This research project was a cooperative effort between the USDA-ARS and the Mississippi Agricultural and Forestry Experiment Station. For more information, contact Dr. McCarty at (662) 323-2230 or jcm@ra.msstate.edu. This publication was edited and designed by Robert A. Hearn, publications editor, Office of Agricultural Communications. Abstract Introduction Materials and Methods Results and Discussion References Table 1.   ABSTRACT       Germplasm cannot be fully utilized until it is evaluated for useful traits. The objective of this study was to screen 79 day-neutral primitive accessions of cotton, Gossypium hirsutum L., for resistance to the southern root-knot nematode, Meloidogyne incognita (Kofoid and White) Chitwood race 3. The southern root-knot nematode is a major pest of cotton. Cotton lines were evaluated in a greenhouse test for egg-mass production after being grown for 40 days i n pots inoculated with nematode eggs. None of the lines produced as few egg masses as our highly resistant check M315 RNR. Twenty-four lines had significantly fewer egg masses than highly susceptible M8, an indication they have an intermediate level of re sistance. Evaluations such as these aid in the use of germplasm in breeding programs. INTRODUCTION       The southern root-knot nematode, Meloidogyne incognita (Kofoid and White) Chitwood, is a pest that has a wide host range of plant species. Among these are Upland cotton, Gossypium hirsutum L. Root-knot nem atodes damage roots, affecting the ability of the plant to transport water and nutrients. This damage can result in increased susceptibility to seedling diseases and fusarium wilt [Fusarium oxysporum Schleft. f. sp. vasinfectum (Atk.) Snyd. And Hans] in mature plants.       The development and use of cultivars with resistance to root-knot nematodes could reduce losses in cotton from this nematode and the pathogens that interact with it to cause diseases. Shepherd (1974) developed and relea sed Auburn 623 RNR, which had exceptional resistance to the root-knot nematode; however, it had agronomic deficiencies. The Auburn 623 RNR source of resistance was transferred to elite germplasm lines that had vastly improved agronomic traits (Shepherd et al., 1989, 1996).       In a search for additional sources of resistance, Shepherd (1983) evaluated 471 photoperiodic primitive accessions of cotton and found 18 that were resistant. He subsequently released 12 day-neutral converted germplasm lines (Shepherd et al., 1988).       A program has been in place for a number of years to incorporate day-neutral genes in the primitive accessions of cotton (McCarty et al., 1979). McCarty and Jenkins (1992) reported agronomic and fiber data for 79 access ions, which had been converted to day-neutral flowering types. This report presents root-knot nematode screening data for these 79 accessions. MATERIALS AND METHODS       The root-knot nematode evaluation was conducted in the greenhouse following methods previously reported by Shepherd (1979). Plants were grown in 8.9x7.6-centimeter (diameter by depth) plastic pots filled with fumigated Wickham sandy loam soil. Approximately 5,000 root-knot nematode eggs were deposited into a 2-centimeter hole in the center of each pot. The hole was filled with sand, and the pots were covered for 7 days with sequential layers of plastic, brown paper, and aluminum foil to allow the eggs to hatch and the juveniles to disperse. After 7 days, the covering was removed, and one seed was planted in each pot. The covering was placed over the bed for an additional 3 days and then removed. This step minimized mois ture loss while the seed germinated. The pots were arranged in a randomized complete block design with cotton lines as treatments. The test consisted of three five-plant replications, with each plant in a separate pot. Seventy-nine (BC4F5) day-neutral pri mitive accessions and two checks were grown in this test. These day-neutral accessions had previously been released as germplasm lines (McCarty and Jenkins 1993). M8 was used as the susceptible check and M315 RNR as the resistant check.       Approximately 40 days after planting, the plants were excised about 5 centimeters above the soil line. Roots were washed with a high-volume, low-pressure spray of water to remove the soil. The roots were then placed in plastic containers filled with water by cotton line.       The number of egg masses per plant was used to determine the resistance level of the cotton lines tested. The excised roots were placed in a Phloxine B solution for 15 minutes and then rinsed. The egg masses were staine d a pinkish-red, which aided in making counts. Egg masses were counted and recorded for each plant. RESULTS AND DISCUSSION       The results of the root-knot nematode screen are presented in Table 1. None of the day-neutral lines were as resistant as M315 RNR. M315 RNR is a highly resistant germplasm line (Shepherd et al., 1 989, 1996). Twenty-four day-neutral lines had significantly fewer egg masses than highly susceptible M8.       Shepherd (1983) evaluated the photoperiodic version of most of these primitive accessions and found them to be susceptible. He rated accession T78 as being resistant andT247 and T255 as being intermediate in resistance in his study based on a galling and a reproduction index.       In our screen, the day-neutral versions of these accessions were rated as intermediate to resistant. During our day-neutral conversion process, we did not practice any selection other than for the flowering trait.       The egg mass number for most of the day-neutral accessions was not different from the susceptible check M8. This was in agreement with what Shepherd (1983) reported for the photoperiodic accessions.       Germplasm must be evaluated for useful traits before it can be fully utilized. Evaluations, such as the one reported here, aid plant breeders in making germplasm selections for breeding programs. This research is part o f an ongoing ARS research program to evaluate race stock germplasm for useful traits and make this information available to the germplasm system. The lines reported here have been converted from photoperiodic to day-neutral and released to breeders for us e. These evaluations on reaction to root-knot nematode generate knowledge that is crucial when germplasm is used in crosses to improve upland cotton cultivars. Table 1. Average number of root-knot nematode egg masses per plant in day-neutral primitive cotton lines, M8 (susceptible check), and M315 (resistant check). Entry Egg masses per plant Entry Egg masses per plant Entry Egg masses per plant T-2DN 122 T-87DN 117 T-174DN 140 T-7DN 144 T-88DN 102 T-175DN 114 T-17DN 145 T-91DN 138 T-180DN 103 T-24DN   90 T-96DN 101 T-182DN 165 T-30DN 140 T-100DN 100 T-197DN   61 T-31DN   95 T-101DN 104 T-206DN 140 T-32DN 145 T-102DN 117 T-212DN 147 T-33DN 153 T-104DN 116 T-215DN   66 T-36DN 114 T-106DN   79 T-226DN 113 T-40DN 117 T-113DN 128 T-228DN 140 T-43DN 136 T-117DN 107 T-237DN 132 T-45DN 108 T-119DN   95 T-239DN 105 T-48DN 118 T-120DN 108 T-243DN   99 T-53DN 105 T-121DN 146 T-244DN 105 T-55DN 117 T-124DN 115 T-245DN 127 T-57DN   76 T-140DN 114 T-247DN   92 T-60DN 130 T-150DN 131 T-257DN   98 T-61DN 130 T-151DN 163 T-326DN 164 T-62DN   93 T-154DN 119 T-570DN 137 T-63DN 100 T-155DN 106 T-612DN 127 T-67DN 108 T-156DN 144 T-633DN 115 T-68DN 111 T-158DN 140 T-634DN 116 T-72DN 138 T-162DN 118 T-641DN 147 T-74DN 138 T-164DN 112 T-1000DN 152 T-76DN 155 T-165DN   94 T-1149DN 124 T-77DN 110 T-168DN 134 M8 149 T-78DN   77 T-170DN 116 M315 RNR    3 LSD 0.05   41 References McCarty, J.C., Jr., J.N. Jenkins, W.L. Parrott, and R.G. Creech. 1979. The conversion of photoperiodic primitive race stocks of cotton to day-neutral stocks. Mississippi Agricultural and Forestry Experiment Station Research Report 4(19):4. McCarty, J.C., Jr., and J.N. Jenkins. 1992. Characteristics of 79 day-neutral primitive race accessions. Mississippi Agricultural and Forestry Experiment Station Technical Bulletin 184. McCarty, J.C., Jr., and J.N. Jenkins. 1993. Registration of 79 day-neutral primitive cotton germplasm lines. Crop Science 33:351. Shepherd, R.L. 1974. Transgressive segregation for root-knot nematode resistance in cotton. Crop Science 14:872-875. Shepherd, R.L. 1979. A quantitative technique for evaluating cotton for root-knot nematode resistance. Phytopathology 69:427-430. Shepherd, R.L. 1983. New sources of resistance to root-knot nematodes among primitive cotton. Crop Science 23:999-1002. Shepherd, R.L., J.C. McCarty, Jr., J. Jenkins and W.L. Parrott. 1988. Registration of twelve nonphotoperiodic lines with root-knot nematode resistant primitive cotton germplasm. Crop Science 28:868-869. Shepherd, R.L., W.L. Parrott, J.C. McCarty, Jr., and J. Jenkins. 1989. Notice of release of nine root-knot nematode resistant germplasm lines of upland cotton Gossypium hirsutum L. USDA/Mississippi Agricultural and Forestry Experiment Statio n Memo. Shepherd, R.L., J.C. McCarty, Jr., J. Jenkins and W.L. Parrott. 1996. Registration of nine cotton germplasm resistant to root-knot nematode. Crop Science 36:820. Mention of a trademark or proprietary product does not constitute a guarantee or warranty of the product by the Mississippi Agricultural and Forestry Experiment Station and does not imply its approval to the exclusion of other products that also may be su itable. Mississippi State University does not discriminate on the basis of race, color, religion, national origin, sex, age, disability, or veteran status.   Visit: DAFVM || USDA Search our Site || Need more information about this subject? Last Modified: Thursday, 03-Oct-02 09:03:58 URL: http://msucares.com/pubs/researchreports/rr22-3.htm Mississippi State University is an equal opportunity institution. Recommendations on this web site do not endorse any commercial products or trade names.