S1092: Biology, ecology, and management of emerging nematode threats in the Southern United States.
(Multistate Research Project)
Climate change, drought, increase production costs and chemical resistant weeds/pathogens challenges agricultural production each year. In addition, customers are demanding accountability and more sustainable, environmentally conscious agricultural practices. To accomplish more efficient food and fiber production, disease management cannot be overlooked. Plant-parasitic nematodes (PPN) causes on average 10% losses (USDA, 2020). Not only do PPN causes yield and economical losses, but they are also a venue used by secondary pathogen to cause disease, resulting in greater losses. The report, dissemination and increase in incidence of new nematodes may threat the production of many crops in the USA.
The research in this proposal addresses important agricultural crop management issues as identified by the REE Advisory Board. In the Report on Agriculture Research Needs of Commodity Crops, the REE Advisory Board states that sustainable, efficient production of these staples (including cotton, soybean, and peanut) is critical to the US food supply and economy, and that “productive efficiency” must be a top priority in order to meet the demands of a growing population in the US and the world. Movement of agricultural goods across the nation and internationally has brought new challenges. The dissemination, dispersal, and movement of new PPN can represent a limitation to major agricultural production in the nation. Further, climate change is likely to affect the distribution of nematode species, as warmer weather allows nematodes to infect crops earlier in the season causing greater damage.
Nematode species such as Heterodera glycines, Meloidogyne hapla, M. floridensis and M. enterolobii have been reported in the last decade in new crops and locations (Rutter et al., 2019; Westphal et al., 2019; Ye et al., 2013; 2019). Emerging nematode species can spread to new geographical regions by self-dispersal, natural and human-assisted dispersal (Jones, 1980; Lehman, 1994). The microscopic size, rapid life cycle, high fecundity, broad host range of some species, and development of non-descript foliar symptoms allow for movement of PPNs to frequently go unnoticed until population establishment is well advanced (Ferris et al., 2003; Singh et al., 2013). Several plant disease management strategies may be considered for limiting dissemination of PPNs to new geographic areas, discouraging their establishment, or reducing endemic populations. These strategies include exclusion, containment and eradication, and management of established populations (Ferris et al., 2003; Barker, 1997). Robust and successful nematode management programs frequently incorporate more than one tactics from several control strategies (Bridge, 1996; Barker and Koenning, 1998; Verdejo-Lucas and McKenry, 2004). Cultural practices, the use of resistant varieties and chemical control can be combined to manage nematodes.
Increasingly, there are emerging threatens to crop production from PPN damage. These emerging threats result from geographic range expansion of nematodes—including invasive nematodes—, infestation of endemic nematodes on new crops due to nematode adaptation or introduction of new crops, and break-down of traditional management tactics due to loss of management products or nematode adaptation. Examples of emerging nematode threats in each category follow. In the case of invasive nematodes, Meloidogyne enterolobii (M.e.) is a critical concern. Meloidogyne enterolobii was discovered in China (Yang and Eisenback, 1983), earned its name of "guava root-knot nematode" by devastating guava orchards in Brazil (Gomes et al., 2012), and was discovered in Florida in 2001 (Brito et al., 2004). Since that time, it has spread to other states in the Southeast including North Carolina in 2011, and Louisiana and South Carolina in 2018 (Rutter, Skantar et al., 2019; Ye et al., 2013). M.e. is of great concern because it is more aggressive—symptoms may be more severe and damage potential is greater—than other root-knot nematodes (Brito et al., 2004; Gomes et al., 2012). Additionally, it can reproduce on many cultivars with resistance to root-knot nematodes, a primary management tactic for root-knot nematodes (Kiewnick et al., 2009; Rutter, Wadl et al., 2019). Southern farmers face substantial risk from this nematode due to direct damage to crops and related economic pressures due to quarantines. A more mature example of nematode range expansion is the reniform nematode (Rotylenchulus reniformis). Reniform nematode was detected in the continental US in the 1940s. Since then, it spread to Mississippi and South Carolina in the 1960s, Arkansas and North Carolina in the 1980s, and is now the most limiting nematode pest in US cotton production (Robinson, 2007).
Nematode populations have changed over time, such is the case of endemic nematodes reported in new crops, and emerging nematode in new geographical areas due to change in management practices. An example of an endemic nematode affecting a new crop is the sting nematode (Belonolaimus longicaudatus) affecting peanut production in Florida and Georgia. Sting nematode is highly damaging to a wide range of crops, but until recently it was not known to affect peanut, severely reducing shoot and root growth to the point of killing plants. In 2015, severe damage in commercial peanut fields in Levy County, Florida due to sting nematode was reported (Kutsuwa et al., 2015). An example of emerging nematode problems due to changing management practices or crop production is the southern root-knot nematode (Meloidogyne incognita, SRKN) in Mid-South states like Arkansas. In Arkansas, SRKN was of little importance in the 1980 as it was only detected in an average of 3.2% of samples received from 1978-1986 to the nematode diagnostic lab, compared to 36% in a more recent survey (Robbins et al., 1987; Kirkpatrick and Sullivan, 2018). An increase in SRKN-susceptible soybean cultivars and the addition of corn into Mid-South cropping system are two important factors that have made southern root-knot nematode an emerging threat there.